add option to specify path for rubocop and usage in relative beautifier

src/beautifiers/rubocop.coffee

@@ -15,7 +15,6 @@ module.exports = class Rubocop extends Beautifier
 
   beautify: (text, language, options) ->
 
-    path = require 'path'
     fs = require 'fs'
 
     configFile = path.join(atom.project.getPaths()[0], ".rubocop.yml")
@@ -33,11 +32,34 @@ module.exports = class Rubocop extends Beautifier
       configFile = @tempFile("rubocop-config", yaml.safeDump(config))
       @debug("rubocop", config, configFile)
 
-    @run("rubocop", [
-      "--auto-correct"
-      "--config", configFile
-      tempFile = @tempFile("temp", text)
-      ], {ignoreReturnCode: true})
-      .then(=>
-        @readFile(tempFile)
-      )
+    @Promise.all([
+      @which(options.rubocop_path) if options.rubocop_path
+      @which('rubocop')
+    ]).then((paths) =>
+      @debug('php-cs-fixer paths', paths)
+      _ = require 'lodash'
+      path = require 'path'
+      # Get first valid, absolute path
+      rubocopPath = _.find(paths, (p) -> p and path.isAbsolute(p) )
+      @verbose('rubocopPath', rubocopPath)
+      @debug('rubocopPath', rubocopPath, paths)
+      # Check if PHP-CS-Fixer path was found
+      if rubocopPath?
+        @run("rubocop", [
+          rubocopPath
+          "--auto-correct"
+          "--config", configFile
+          tempFile = @tempFile("temp", text)
+          ], {ignoreReturnCode: true})
+          .then(=>
+            @readFile(tempFile)
+          )
+      else
+        @run("rubocop", [
+          "--auto-correct"
+          "--config", configFile
+          tempFile = @tempFile("temp", text)
+          ], {ignoreReturnCode: true})
+          .then(=>
+            @readFile(tempFile)
+          )

src/languages/ruby.coffee

@@ -32,6 +32,11 @@ module.exports = {
       default: defaultIndentSize
       minimum: 0
       description: "Indentation size/length"
+    rubocop_path:
+      title: "Rubocop Path"
+      type: 'string'
+      default: ""
+      description: "Path to the `rubocop` CLI executable"
     indent_char:
       type: 'string'
       default: defaultIndentChar