Move back to using YoastSEO from the repository

Babel can't handle files that have been compiled previously by
Babel because it contains too much duplication. Luckily the source
of the YoastSEO library is still available in the repository which
Babel can use with webpack to compile just fine.

See Yoast/YoastSEO.js#1687 (comment)

lib/app.js

@@ -6,21 +6,19 @@ import {
   string,
 } from 'yoastseo';
 
+// Import the following 'private' classes
+// TODO: This should probably be public: https://github.com/Yoast/YoastSEO.js/issues/1878
+import SEOAssessor from 'yoastseo/src/seoAssessor';
+// TODO: We should replace this with our own presenter.
+import AssessorPresenter from 'yoastseo/src/renderers/AssessorPresenter';
+
 // TODO: Either depend on lodash or don't use this.
 import _ from 'lodash';
 
 const defaultsDeep  = _.defaultsDeep;
 const isObject      = _.isObject;
 const isUndefined   = _.isUndefined;
 
-// Import the following 'private' classes
-// TODO: This should probably be public: https://github.com/Yoast/YoastSEO.js/issues/1878
-// const SEOAssessor                 = require( "yoastseo/js/seoAssessor.js");
-const SEOAssessor = {};
-// TODO: We should replace this with our own presenter.
-// const AssessorPresenter           = require( "yoastseo/js/renderers/AssessorPresenter.js" );
-const AssessorPresenter = {};
-
 const removeHtmlBlocks = string.removeHtmlBlocks;
 
 /**

package.json

@@ -10,7 +10,7 @@
     "build:development": "webpack --mode development"
   },
   "dependencies": {
-    "yoastseo": "^1.40"
+    "yoastseo": "Yoast/YoastSEO.js"
   },
   "devDependencies": {
     "@babel/core": "^7.1.2",

yarn.lock

@@ -3805,10 +3805,9 @@ yargs@^12.0.2:
     y18n "^3.2.1 || ^4.0.0"
     yargs-parser "^10.1.0"
 
-yoastseo@^1.40:
-  version "1.40.0"
-  resolved "https://registry.yarnpkg.com/yoastseo/-/yoastseo-1.40.0.tgz#2be3b91422ddc614131ab4b6e5aab9e6c347170d"
-  integrity sha512-sA4KEi3CHsajG+wzj4oXBhAYb2B2BpM2hWitqyD7URgFJxwrC3PvNFhTF64haE71xx/xxQZKQEODT2iJRe1lAA==
+yoastseo@Yoast/YoastSEO.js:
+  version "1.41.0"
+  resolved "https://codeload.github.com/Yoast/YoastSEO.js/tar.gz/5799f87432fda39e08f9dd2f71ab0d2bf5f3cebe"
   dependencies:
     htmlparser2 "^3.9.2"
     jed "^1.1.0"