fix gemspec and update changelog for missing 1.4.0 release
update to reflect Buff::Boolean change
Specify a version of RSpec

As 3.0.0 of rspec has come out, we suffer from a number of deprecations. A `bundle install was installing
2.99, which is affected by https://github.com/rspec/rspec-mocks/issues/698. Due to the way we freeze so many objects
we hit this error quite a bit with our mocks.
Merge pull request #719 from RiotGames/fix_gem_deps

fix gemspec and update changelog for missing 1.4.0 release