fix invalid result of findXxxxToken methods when value is provided

When you provide both type and value to the `JsFile.findNextToken` method, it will return the first token matching the type without checking the value because of the `prevToken.type !== type` condition.
The same applies to both `JsFile.findNextToken` and `JsFile.findPrevToken`

Let me know if something if wrong :)
this and the next line are repeated in each `it`. You should extract them out to a `describe` with a `beforeEach` to avoid duplicating the setup each time.