Add an scss linter that requires the scss_lint gem

package.json

@@ -28,7 +28,8 @@
     "gulp-svgmin": "^1.2.2",
     "gulp-uglify": "^1.5.3",
     "gulp-util": "^3.0.4",
-    "lodash": "^4.6.1"
+    "lodash": "^4.6.1",
+    "shelljs": "^0.6.0"
   },
   "repository": {
     "type": "git",

tasks/sass.js

@@ -1,18 +1,26 @@
 'use strict';
 
 module.exports = function(gulp, config) {
+
+    var shelljs = require('shelljs');
+    var util = require('gulp-util');
+    if (shelljs.which('scss-lint') !== null) {
+        var scssLint = require('gulp-scss-lint');
+    } else {
+        var scssLint = util.noop;
+        util.log(util.colors.red("SCSS linting is disabled"),"to enable this feature please install scss_lint '", util.colors.green("gem install scss_lint"), "'");
+    }
+
     return function() {
 
         /* define required plugins */
         var sourcemaps = require('gulp-sourcemaps');
-        var util = require('gulp-util');
         var sass = require('gulp-sass');
         var plumber = require('gulp-plumber');
         var autoprefixer = require('gulp-autoprefixer');
         var gulpIf = require('gulp-if');
         var moreCss = require('gulp-more-css');
         var livereload = require('gulp-livereload');
-        var scssLint = require('gulp-scss-lint');
 
         /* function to run on execution */
         return gulp.src(config.sass.src)