fix: Don't attempt to remove an unmapped file.

I'm not really sure what the root cause is here, so this is a bit of a bandaid. When using IntelliJ I see it trying to remove files such as /Users/rob/.../tests/integration/TrackingIntegrationTests.js___jb_old___ even though I've configured just to map *.js.
Merge pull request #3 from rbarreca/fix-dont-remove-unmapped-file

fix: Don't attempt to remove an unmapped file.