(PUP-2014) Make gem provider match on a single gem name

Currently the gem provider will match gemname$, for example with bundler
this will return quite a long list of anything ending with bundler. When
a match returns a longer list, it will actually connect and try to pull
the latest gem again, thus increasing the WAN usage and rubygems.org
usage when not necessary.

The proposed fix adds a ^ in front of the name var to ensure it begins
with the gemname.