Improve error message for missing json property in constructor

[rozele]

Given the following:

new JSONPath({ path: "$" })

The error message is:

You must supply a "path" property when providing an object argument to JSONPath.evaluate().

It should probably be:

You must supply a "json" property when providing an object argument to JSONPath.evaluate().

[brettz9]

Added in v2.0.0. Thanks for the report.

Note that if json is present but undefined, it will still not throw, as there is the potential one is trying to query undefined.