Avoid warning message when installing gem

Avoid:
Failures:

  1) Verify required rspec dependencies passes when libraries are required
     Got 1 failure and 1 other error:

     1.1) Failure/Error: expect(`bundle exec #{script} 2>&1`).to be_empty
            expected `"WARNING:  open-ended dependency on activesupport (>= 4.2) is not recommended\n  if activesupport is ... 'railties', '~> 4.2'\nWARNING:  See http://guides.rubygems.org/specification-reference/ for help\n".empty?` to return true, got false

Author: benoittgt

rspec-rails.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |s|
     s.cert_chain = [File.expand_path('~/.gem/rspec-gem-public_cert.pem')]
   end
 
-  version_string = ['>= 4.2']
+  version_string = ['>= 4.2', '< 7.0']
 
   s.add_runtime_dependency %q<activesupport>, version_string
   s.add_runtime_dependency %q<actionpack>,    version_string