Match pact js lint

[TimothyJones]

This is like https://github.com/pact-foundation/pact-js-core/pull/425 and https://github.com/pact-foundation/pact-js/pull/1027 - it simply tightens the lint settings to match pact-js and pact-js core.

Key points:

• This is a Jest project, so it uses jest settings rather than mocha.
  • If you use this as a base for other jest projects, make sure you enable jest/expect-expect - it is only disabled because we have tests that always throw to test "this shouldn't run"
• Also I tightened the tsconfig settings to match pact-js-core
• Some code is now duplicated because you can't import from tests (this results in the tests being run twice). An improvement would be to have a __fixtures__ or something that the build skips.

[TimothyJones]

Doing the same treatment to mocha pact is left as an exercise for the reader

[YOU54F]

Thanks @TimothyJones, this looks good, would you be able to resolve the conflicts and we can get this merged :)