Update "rest" to "cl-rest"

[dreac0nic]

Similar to my previous merge request #8 when installing flycheck-clang-analyzer via MELPA (20180215.345) with GNU emacs 25.3.1. Emacs reports rest as undefined. I changed this to the cl-lib defined cl-rest which should function identically.

I'm not sure if this change will effect backwards compatibility with those who have rest defined. If a strain of emacs still uses rest perhaps a more platform-free implementation would be better (perhaps an implementation using &rest).

[alexmurray]

Thanks.