Update version constraint for jsonapi-renderer

Currently (2017-02-20) the latest version is 0.1.2.

Why not use a version constraint like '~> 0.1.1'? Because
we know of no reason why 0.1.1.beta1 cannot still be used.
That said, we have done no research looking for such a reason.

active_model_serializers.gemspec

@@ -42,8 +42,7 @@ Gem::Specification.new do |spec|
   # 'minitest'
   # 'thread_safe'
 
-  # TODO: Latest jsonapi-renderer is 0.1.2
-  spec.add_runtime_dependency 'jsonapi-renderer', '0.1.1.beta1'
+  spec.add_runtime_dependency 'jsonapi-renderer', ['>= 0.1.1.beta1', '< 0.2']
   spec.add_runtime_dependency 'case_transform', '>= 0.2'
 
   spec.add_development_dependency 'activerecord', rails_versions