Set required_ruby_version

shopify_api.gemspec

@@ -23,8 +23,10 @@ Gem::Specification.new do |s|
   s.summary = %q{ShopifyAPI is a lightweight gem for accessing the Shopify admin REST web services}
   s.license = "MIT"
 
-  s.add_dependency("activeresource", ">= 3.0.0")
-  s.add_dependency("rack")
+  s.required_ruby_version = ">= 2.3"
+
+  s.add_runtime_dependency("activeresource", ">= 3.0.0")
+  s.add_runtime_dependency("rack")
 
   s.add_development_dependency("mocha", ">= 0.9.8")
   s.add_development_dependency("fakeweb")