If we don't pass an enumerable we assume we want to increment the given property by 1, just like the JS client
Merge branch 'fixes_increment_with_single_value' of github.com:sourcery/mixpanel-ruby into sourcery-fixes_increment_with_single_value
Use a separate method instead of overloading
Version bump for addition of plus_one
Merge branch 'master' of github.com:mixpanel/mixpanel-ruby