Fix race in tests and eliminate symlinks

We were (sometimes) updating the watched file before the Listen thread
was fully set up, meaning Listen couldn't detect the change, and our
test would time out (happened especially often against 1.8).

Eliminate the race, and enable Travis on 1.8 and 2.0.

Also ensure we never use symlinks as they can make Listen cranky.
Merge pull request #8 from dmarcotte/test-race

Fix race in tests and eliminate symlinks