Improve description of CI types node and in specs

lib/gitlab/ci/config/node/global.rb

@@ -28,7 +28,7 @@ module Gitlab
             description: 'Configuration of stages for this pipeline.'
 
           node :types, Node::Stages,
-            description: 'Stages for this pipeline (deprecated key).'
+            description: 'Deprecated: stages for this pipeline.'
 
           node :cache, Node::Cache,
             description: 'Configure caching between build jobs.'

spec/lib/gitlab/ci/config/node/undefined_spec.rb

@@ -27,13 +27,13 @@ describe Gitlab::Ci::Config::Node::Undefined do
       allow(entry).to receive(:default).and_return('some value')
     end
 
-    it 'returns default value for entry that is undefined' do
+    it 'returns default value for entry' do
       expect(undefined.value).to eq 'some value'
     end
   end
 
   describe '#undefined?' do
-    it 'is not a concrete entry that is defined' do
+    it 'is not a defined entry' do
       expect(undefined.defined?).to be false
     end
   end