Adding specs for json-schema-matcher gem

- Tested against inline schema that defines a JSON string
- Not testing JSON::Validator. This commit adds specs to test the
  matcher that uses the validator.
A few updates and added specs

- Updated confusing name in spec. Variable name matches spec better.
- Added spec to explicitly test that the JSON::Validator is called
  correctly.
Merge pull request #3 from jgdreyes/jr/adding_specs

Adding specs for json-schema-matcher gem