Data is valid against more than one schema from \'oneOf\

[sarangan12]

Repro Steps:

node cli.js validate-example https://github.com/Azure/azure-rest-api-specs/blob/master/specification/search/data-plane/Microsoft.Azure.Search.Service/preview/2017-11-11/searchservice.json

Sample Error:

......
code: 'ONE_OF_MISSING',
            params: [],
            message: 'Data does not match any schemas from \'oneOf\'',
            path: [ 'fields', '1' ],
            inner: 
             [ { code: 'ONE_OF_MULTIPLE',
                 params: [],
                 message: 'Data is valid against more than one schema from \'oneOf\'',
                 path: [ 'fields', '1', 'analyzer' ] },
               { code: 'INVALID_TYPE',
                 params: [ 'null', 'object' ],
                 message: 'Expected type null but found type object',
                 path: [ 'fields', '1' ] } ] },
          { code: 'ONE_OF_MISSING',
.........

Related to #234