Add ruby-head to travis allow failures list
Upgrade gem dependencies
Update travis config to exclude 1.9.2 and use ci:metrics

* This code does not yet pass with mutant, and there is little point
  in failing the build when there are uncovered mutations until
  100% mutation coverage is reached. For now run all other metrics
  for each build.
Merge branch 'master' into axiom-types-refactor

Conflicts:
	axiom.gemspec