maint - modernize the travis configuration

Add additional mcollective gem versions into the matrix, and switch use of
the mcollective gem to the Puppet Labs released mcollective-client gem.
Merge pull request #10 from richardc/modernize-travis

maint - modernize the travis configuration
MCOP-55 - don't treat empty results as though they're not empty

Array#max on an empty array will return nil, which then will cause
the error:

    undefined method `+' for nil:NilClass (NoMethodError)

Here we gate the results processing on getting a populated results
set.