* Bump Racc to 1.8.0 (#1018)

Racc 1.8.0 has been released and this PR bumps Racc to 1.8.0:
https://github.com/ruby/racc/releases/tag/v1.8.0

Author: koic

Gemfile

@@ -8,4 +8,4 @@ gemspec
 # Workaround for bug in Bundler on JRuby
 # See https://github.com/bundler/bundler/issues/4157
 gem 'ast', '>= 1.1', '< 3.0'
-gem 'racc', '1.7.3'
+gem 'racc', '1.8.0'