Update `Gitlab.com?` to support staging

lib/gitlab.rb

@@ -2,6 +2,11 @@ require_dependency 'gitlab/git'
 
 module Gitlab
   def self.com?
-    Gitlab.config.gitlab.url == 'https://gitlab.com'
+    # Check `staging?` as well to keep parity with gitlab.com
+    Gitlab.config.gitlab.url == 'https://gitlab.com' || staging?
+  end
+
+  def self.staging?
+    Gitlab.config.gitlab.url == 'https://staging.gitlab.com'
   end
 end

spec/lib/gitlab_spec.rb

@@ -8,6 +8,12 @@ describe Gitlab, lib: true do
       expect(described_class.com?).to eq true
     end
 
+    it 'is true when on staging' do
+      stub_config_setting(url: 'https://staging.gitlab.com')
+
+      expect(described_class.com?).to eq true
+    end
+
     it 'is false when not on GitLab.com' do
       stub_config_setting(url: 'http://example.com')