Remove Active Resource upper bound version

Upper bound versions should be avoided because they only make harder for applications to upgrade
the libraries.

Author: rafaelfranca

shopify_api.gemspec

@@ -32,7 +32,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = ">= 2.4"
 
-  s.add_runtime_dependency("activeresource", ">= 4.1.0", "< 6.0.0")
+  s.add_runtime_dependency("activeresource", ">= 4.1.0")
   s.add_runtime_dependency("rack")
   s.add_runtime_dependency("graphql-client")