Remove the bigdecimal gem dependency

This does not seem to be used in the existing source code, so I am
going to try out removing it. It seems to be causing an error during
TravisCI execution, and this should fix it.
Add git config commands to the test runner

This will ensure that the cloned repositories will have user and email
configured, and not depend upon those values being configured for
either the user or the system where the test is being run.
Exclude metric_fu dependency based on ruby version

metric_fu includes the can gem which will not work with Ruby1.8.
By excluding it for 1.8 builds, then we can test the gem under Ruby1.8
with TravisCI.