Expand jsonschema requirements to <4

[Code0x58]

This expands the range of allowed jsonschema versions as 3.0.0+ versions have been around for over 6 months.

It looks like the only change is that the default jsonschema draft went from version 4 to 7 [changelog][diff], so this PR explicitly uses 4 to avoid the need to look into more changes.

The test failures appear to be down to flaking being addressed in #1447

Test error report

=================================== FAILURES ===================================
________________ TestParityShhModuleTest.test_shh_remove_filter ________________

self = <parity.test_parity_ws.TestParityShhModuleTest object at 0x7f85f31503d0>
web3 = <web3.main.Web3 object at 0x7f85f2ec5690>

    def test_shh_remove_filter(self, web3):
        receiver = web3.parity.shh.newKeyPair()
        receiver_pub = web3.parity.shh.getPublicKey(receiver)
    
        payload = web3.toHex(text="test message :)")
        topic = '0x13370000'
        shh_filter = web3.parity.shh.newMessageFilter({'decryptWith': None, 'topics': [topic]})
    
>       assert web3.parity.shh.post({
            'payload': payload,
            'topics': [topic],
            'to': {'public': receiver_pub},
            'priority': 500,
            'ttl': 400,
        })

payload    = '0x74657374206d657373616765203a29'
receiver   = '0x71452d27dd134d5ab03f1fd38628f827dcd5f4c350b08edcfd449b229f8b3ddd'
receiver_pub = '0x52d49e6d285c16c0ef8ab912b578894d591740484ae64b21762e4b3599621f4708a8b99b9d73cdb0c8f1ed79b614877c5fd7852170d82eb03e821360f7125611'
self       = <parity.test_parity_ws.TestParityShhModuleTest object at 0x7f85f31503d0>
shh_filter = '0x179c5a9472c1f9b23dc3defd9dd3155bb009d3e564652cafc6ffc85f3c50bfdb'
topic      = '0x13370000'
web3       = <web3.main.Web3 object at 0x7f85f2ec5690>

web3/_utils/module_testing/shh_module.py:323: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
web3/module.py:12: in caller
    w3.manager.request_blocking(method_str, params),
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <web3.manager.RequestManager object at 0x7f85f2ec5250>
method = 'shh_post'
params = ({'payload': '0x74657374206d657373616765203a29', 'priority': 500, 'to': {'public': '0x52d49e6d285c16c0ef8ab912b578894d...b21762e4b3599621f4708a8b99b9d73cdb0c8f1ed79b614877c5fd7852170d82eb03e821360f7125611'}, 'topics': ['0x13370000'], ...},)

    def request_blocking(self, method, params):
        """
        Make a synchronous request using the provider
        """
        response = self._make_request(method, params)
    
        if "error" in response:
>           raise ValueError(response["error"])
E           ValueError: {'code': -32085, 'message': 'PoW too low to compete with other messages'}

method     = 'shh_post'
params     = ({'payload': '0x74657374206d657373616765203a29', 'priority': 500, 'to': {'public': '0x52d49e6d285c16c0ef8ab912b578894d...b21762e4b3599621f4708a8b99b9d73cdb0c8f1ed79b614877c5fd7852170d82eb03e821360f7125611'}, 'topics': ['0x13370000'], ...},)
response   = {'error': {'code': -32085, 'message': 'PoW too low to compete with other messages'}, 'id': 243, 'jsonrpc': '2.0'}
self       = <web3.manager.RequestManager object at 0x7f85f2ec5250>

web3/manager.py:97: ValueError
____________________ TestParityShhModuleTest.test_shh_post _____________________

self = <parity.test_parity_ws.TestParityShhModuleTest object at 0x7f85d8418790>
web3 = <web3.main.Web3 object at 0x7f85f2ec5690>

    def test_shh_post(self, web3):
        sender = web3.parity.shh.newKeyPair()
>       assert web3.parity.shh.post({
            "topics": ["0x12345678"],
            "payload": web3.toHex(text="testing shh on web3.py"),
            "from": sender,
            "priority": 40,
            "ttl": 400,
        })

self       = <parity.test_parity_ws.TestParityShhModuleTest object at 0x7f85d8418790>
sender     = '0x4326bbe69c16d362bb6417ca5599c57a4b36072e3cfae82b2825d3d701116204'
web3       = <web3.main.Web3 object at 0x7f85f2ec5690>

web3/_utils/module_testing/shh_module.py:380: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
web3/module.py:12: in caller
    w3.manager.request_blocking(method_str, params),
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <web3.manager.RequestManager object at 0x7f85f2ec5250>
method = 'shh_post'
params = ({'from': '0x4326bbe69c16d362bb6417ca5599c57a4b36072e3cfae82b2825d3d701116204', 'payload': '0x74657374696e6720736868206f6e20776562332e7079', 'priority': 40, 'topics': ['0x12345678'], ...},)

    def request_blocking(self, method, params):
        """
        Make a synchronous request using the provider
        """
        response = self._make_request(method, params)
    
        if "error" in response:
>           raise ValueError(response["error"])
E           ValueError: {'code': -32085, 'message': 'PoW too low to compete with other messages'}

method     = 'shh_post'
params     = ({'from': '0x4326bbe69c16d362bb6417ca5599c57a4b36072e3cfae82b2825d3d701116204', 'payload': '0x74657374696e6720736868206f6e20776562332e7079', 'priority': 40, 'topics': ['0x12345678'], ...},)
response   = {'error': {'code': -32085, 'message': 'PoW too low to compete with other messages'}, 'id': 258, 'jsonrpc': '2.0'}
self       = <web3.manager.RequestManager object at 0x7f85f2ec5250>

web3/manager.py:97: ValueError

Cute animal picture

web3.py/CONTRIBUTING.md

Lines 10 to 14 in 4a98f1a

	# Cute Animal Pictures
	All pull requests need to have a cute animal picture. This is a very important
	part of the development process.

[kclowes]

Thanks @Code0x58! This looks good to me!