Add explanation of threshold to README.
Rubygems broke builds on Ruby 1.8.7: travis-ci/travis-ci#1793 rubygems/rubygems#763 This patch is a temporary workaround until rubygems is updated.
Add Ruby 1.8.7 compatibility
Implement new recommendations from rubocop
Conflicts: README.md config/flay.yml spec/unit/yardstick/config/for_rule_spec.rb spec/unit/yardstick/rule/class_methods/coerce_spec.rb spec/unit/yardstick/rule/enabled_predicate_spec.rb spec/unit/yardstick/rule/initialize_spec.rb spec/unit/yardstick/rule/validatable_predicate_spec.rb
* Update round_percentage to use floor, which will be less forgiving to "almost 100" covered files that were previously being rounded up to 100.