relative_paths now defaults to false (fixes #131)

- Fix issue #131 - `Listener#relative_paths` now defaults to `false`, and added a mention of the errant change to the Changelog for v1.0.0
- Fixed minor mistake in the relevant spec (using `watched_directories` when should have been using `watched_directory` and tried to improve code to make similar mistakes more difficult to make.
- Replace deprecated `mock` with new `double`, and fixed deprecated usage of `raise_error(SPECIFIC_ERROR_CLASS)` (see https://github.com/rspec/rspec-expectations/issues/231)