Add Cask file as Emacs Lisp (#3416)

* Add Cask file as Emacs Lisp

* Replace Cask file (original is zonuexe/composer.el)

lib/linguist/languages.yml

@@ -1121,6 +1121,7 @@ Emacs Lisp:
   - ".gnus"
   - ".spacemacs"
   - ".viper"
+  - Cask
   - Project.ede
   - _emacs
   - abbrev_defs

samples/Emacs Lisp/filenames/Cask

@@ -0,0 +1,9 @@
+(package "composer" "0.0.7" "Interface to PHP Composer")
+(source "melpa" "https://melpa.org/packages/")
+
+(package-file "composer.el")
+
+(depends-on "f")
+(depends-on "s")
+(depends-on "request")
+(depends-on "seq")