Switch Crystal beautifier to using Executables

src/beautifiers/crystal.coffee

@@ -8,24 +8,24 @@ Beautifier = require('./beautifier')
 module.exports = class Crystal extends Beautifier
   name: "Crystal"
   link: "http://crystal-lang.org"
-  isPreInstalled: false
+  executables: [
+    {
+      name: "Crystal"
+      cmd: "crystal"
+      homepage: "http://crystal-lang.org"
+      installation: "https://crystal-lang.org/docs/installation/"
+      version: {
+        parse: (text) -> text.match(/Crystal (\d+\.\d+\.\d+)/)[1]
+      }
+    }
+  ]
 
   options: {
     Crystal: false
   }
 
   beautify: (text, language, options) ->
-    # Seems that Crystal dosen't have Windows support yet.
-    if @isWindows
-      @Promise.reject(@commandNotFoundError(
-        'crystal'
-        {
-        link: "http://crystal-lang.org"
-        program: "crystal"
-        })
-      )
-    else
-      @run("crystal", [
+    @exe("crystal").run([
       'tool',
       'format',
       tempFile = @tempFile("temp", text)