Changed scripts submodule url to its public location. This allows calls
to git submodule update --init to succeed for users without a private key to the
github/yesodweb repository. Prevents the following error message during a call
to cabal-meta install:

Exception: error running: git clone --recursive https://github.com/yesodweb/persistent
exit status: 1
stderr: fatal: unable to connect to github.com:
github.com[0: 192.30.252.131]: errno=Connection timed out

Clone of 'git://github.com/yesodweb/scripts.git' into submodule path 'scripts' failed