Move 1.8.7's Gemfile for subdirectory

Primarily just for Travis CI this is moved to reduce the top level files
when other testing Gemfiles are added.
Fix reference to fog's gemspec
Test the latest edge version of fog and parts

This uses git references to test fog against the latest repos for
extracted parts such as core and providers.
Merge pull request #2789 from fog/edge_gemfile

Adds Gemfile for Travis to test against edge versions of dependencies