required_ruby_version is an assignment and not a method

entitlements-app.gemspec

@@ -11,8 +11,7 @@ Gem::Specification.new do |s|
   s.files = Dir.glob("lib/**/*") + %w[bin/deploy-entitlements VERSION]
   s.homepage = "https://github.com/github/entitlements-app"
   s.executables = %w[deploy-entitlements]
-
-  s.required_ruby_version '~> 2.0'
+  s.required_ruby_version = '~> 2.0'
 
   s.add_dependency "concurrent-ruby", "= 1.1.9"
   s.add_dependency "contracts", "= 0.16.0"