Don't watch vendor directories. Follows #24

[gcmt]

I think that it doesn't really make sense to watch vendor directories if they're excluded from tests anyway. Plus, when launched looper output all watched directories, and with many dependencies this can become quite annoying.

I see from #24 that you wondered about making this change but didn't do it eventually. Do you have any reason for not watching directories that I'm not aware of?

[nathany]

It's a tough call.

I mean, if you actually do change something in a vendor folder, then maybe it makes sense to run the tests?

On the other hand, some people have talked about not even vendoring the tests at all, in which case there would be no point to watching those folders.

[dwlnetnl]

I just opened #33 discussing this issue (sorry about that!) Personally I don't mind to use a flag that will include the vendor directory or use the readline interface to trigger such test.

However I'm a bit wary about a vendor directory that contains a vendor directory by itself? Glide (www.glide.sh) for example will flatten the dependency tree into the top level vendor directory.