Update lodash and remove prototype vulnerabilities

Fixes: https://github.com/sass/node-sass/issues/2574 by removing prototype vulnerabilities for: 

https://ossindex.sonatype.org/component/pkg:npm/lodash.assign

https://ossindex.sonatype.org/component/pkg:npm/lodash.clonedeep

https://ossindex.sonatype.org/component/pkg:npm/lodash.mergewith

lib/index.js

@@ -3,8 +3,8 @@
  */
 
 var path = require('path'),
-  clonedeep = require('lodash.clonedeep'),
-  assign = require('lodash.assign'),
+  clonedeep = require('lodash/cloneDeep'),
+  assign = require('lodash/assign'),
   sass = require('./extensions');
 
 /**

lib/watcher.js

 var grapher = require('sass-graph'),
-  clonedeep = require('lodash.clonedeep'),
+  clonedeep = require('lodash/cloneDeep'),
   path = require('path'),
   config = {},
   watcher = {},

package.json

@@ -60,9 +60,7 @@
     "get-stdin": "^4.0.1",
     "glob": "^7.0.3",
     "in-publish": "^2.0.0",
-    "lodash.assign": "^4.2.0",
-    "lodash.clonedeep": "^4.3.2",
-    "lodash.mergewith": "^4.6.0",
+    "lodash": "^4.17.11",
     "meow": "^3.7.0",
     "mkdirp": "^0.5.1",
     "nan": "^2.10.0",

test/spec.js

@@ -7,8 +7,8 @@ var assert = require('assert'),
       ? require('../lib-cov')
       : require('../lib'),
   readYaml = require('read-yaml'),
-  mergeWith = require('lodash.mergewith'),
-  assign = require('lodash.assign'),
+  mergeWith = require('lodash/mergeWith'),
+  assign = require('lodash/assign'),
   glob = require('glob'),
   specPath = require('sass-spec').dirname.replace(/\\/g, '/'),
   impl = 'libsass',