Fall back to text body

[chawes13]

Note: Changes dependent on #95

Resolves #93

This adds a new option which will determine whether or not to perform a "strict" JSON parse on the response's body. Strict in this sense essentially means response.json().catch(() => null). This will be the default behavior, which matches how the behavior currently works in v4.1.9. If the option is set to false, then a failed parsing will default to returning the text of the body, which will be left to the client to handle appropriately.

The use case that we're intending to solve for here is when a 3rd Party API doesn't escape a string response. E.g.,

getThirdPartyToken() // response: 123AZY
// vs.
getThirdPartyToken() // response: "123AZY"

The first response will fail JSON.parse, while the other will succeed.

This implementation was inspired by Axios' implementation:

[bhennes2]

LGTM! Was a bit turned around on the mockResponse within the http.js file but I follow the ?? operator now.