Use 301 redirect for renamed doc redirections

lib/app.rb

@@ -299,7 +299,7 @@ class App < Sinatra::Application
 
   get %r{\A/([\w~\.%]+)(\-[\w\-]+)?(/.*)?\z} do |doc, type, rest|
     doc.sub! '%7E', '~'
-    return redirect "/#{DOC_REDIRECTS[doc]}#{type}#{rest}" if DOC_REDIRECTS.key?(doc)
+    return redirect "/#{DOC_REDIRECTS[doc]}#{type}#{rest}", 301 if DOC_REDIRECTS.key?(doc)
     return redirect "/angularjs/api#{rest}", 301 if doc == 'angular' && rest.start_with?('/ng')
     return 404 unless @doc = find_doc(doc)