Merge pull request #157 from influxdata/dependabot/bundler/rubocop-tw-1.9.0

Update rubocop requirement from ~> 1.7.0 to ~> 1.9.0

Author: ChrisBr

influxdb-rails.gemspec

@@ -38,7 +38,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rdoc"
   spec.add_development_dependency "rspec"
   spec.add_development_dependency "rspec-rails", ">= 3.0.0"
-  spec.add_development_dependency "rubocop", "~> 1.7.0"
+  spec.add_development_dependency "rubocop", "~> 1.9.0"
   spec.add_development_dependency "sqlite3"
   spec.add_development_dependency "tzinfo"
 end