Improve XML docs: use JSONPath instead of JPath

[304NotModified]

It's important to know how to write the expressions and so we need the proper language name.

JPath gave me confusion, as it's not a common language name and the JPath class in internal. So took me a while why it's references JPath ;)

The tutorial https://www.newtonsoft.com/json/help/html/QueryJsonSelectTokenJsonPath.htm use the "JSONPath", so I used it here instead of JPath.

PS: This is a follow up of https://stackoverflow.com/questions/49981643/is-jpath-the-same-as-jsonpath/58142421