Fix text rendering of readme/index

lib/gitlab/file_detector.rb

@@ -8,7 +8,7 @@ module Gitlab
   module FileDetector
     PATTERNS = {
       # Project files
-      readme: %r{\A(readme|index)[^/]*\z}i,
+      readme: %r{\A(readme|index)(|\.#{Gitlab::MarkupHelper::EXTENSIONS.join('|\.')})$[^\/]*\z}i,
       changelog: %r{\A(changelog|history|changes|news)[^/]*\z}i,
       license: %r{\A((un)?licen[sc]e|copying)(\.[^/]+)?\z}i,
       contributing: %r{\Acontributing[^/]*\z}i,

spec/lib/gitlab/file_detector_spec.rb

@@ -23,6 +23,10 @@ describe Gitlab::FileDetector do
       end
     end
 
+    it 'returns nil for a README.rb file' do
+      expect(described_class.type_of('README.rb')).to be_nil
+    end
+
     it 'returns nil for a README file in a directory' do
       expect(described_class.type_of('foo/README.md')).to be_nil
     end