Use correct github url to find commands.json

Once this is merged:
  - merge the latest changes to commands.json in antirez/redis-doc
  - re-run: utils/generate-command-help.rb > src/help.h

Then we'll have nice and easy tab-completed help in redis-cli again.

Closes #1909

utils/generate-command-help.rb

@@ -50,7 +50,7 @@ def commands
   require "json"
   require "uri"
 
-  url = URI.parse "https://raw.github.com/antirez/redis-doc/master/commands.json"
+  url = URI.parse "https://raw.githubusercontent.com/antirez/redis-doc/master/commands.json"
   client = Net::HTTP.new url.host, url.port
   client.use_ssl = true
   response = client.get url.path