Use new melpa.org address
Update README.md

New Emacs release.
Update prelude-packages.el

New URL, according to http://melpa.org/#/getting-started
Merge pull request #725 from marknsikora/melpa-org

Use new melpa.org address
Merge pull request #726 from biffhero/master

Two quick housekeeping changes
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Update prelude-packages.el
  Update README.md
  Use new melpa.org address