Fix weird gridicons-reader-following.svg

Some tooling knows what to do with the mask, some doesn't. Instead of masking a square, just use the mask as the image like other icons do.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gridicons",
-  "version": "3.4.1-alpha.2",
+  "version": "3.4.1-alpha.3",
   "main": "dist/index.js",
   "files": [
     "dist/",

php/gridicons.php

@@ -467,7 +467,7 @@ function get_gridicon( $gridicon ) {
 			$svg = '<svg class="gridicon gridicons-reader-following-conversation" height="24" width="24" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><g><path d="M16.8 14.5l3.2-3.2V5c0-1.1-.9-2-2-2H4c-1.1 0-2 .9-2 2v9c0 1.1.9 2 2 2h2v5l8.7-8.7 2.1 2.2z"/><path d="M22.6 11.1l-6.1 6.1-2.1-2.2-1.4 1.4 3.5 3.6 7.5-7.6z"/></g></svg>';
 			break;
 		case 'gridicons-reader-following':
-			$svg = '<svg class="gridicon gridicons-reader-following" height="24" width="24" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><g><mask id="a" style="mask-type:alpha" maskUnits="userSpaceOnUse" x="3" y="3" width="21" height="19"><path fill-rule="evenodd" clip-rule="evenodd" d="M21 11.889l-4.455 4.455-2.094-2.176L9.538 19H5c-1.1 0-2-.9-2-2V3h18v8.889zM16.508 22L24 14.482l-1.388-1.376-6.094 6.094-2.106-2.188L13 18.4l3.508 3.6zM9 14H5v-1h4v1zm-4-2h7v-1H5v1zm7-2H5V9h7v1zM5 7h14V5H5v2z"/></mask><g mask="url(#a)"><path d="M1-1h24v24H1z"/></g></g></svg>';
+			$svg = '<svg class="gridicon gridicons-reader-following" height="24" width="24" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><g><path fill-rule="evenodd" clip-rule="evenodd" d="M21 11.889l-4.455 4.455-2.094-2.176L9.538 19H5c-1.1 0-2-.9-2-2V3h18v8.889zM16.508 22L24 14.482l-1.388-1.376-6.094 6.094-2.106-2.188L13 18.4l3.508 3.6zM9 14H5v-1h4v1zm-4-2h7v-1H5v1zm7-2H5V9h7v1zM5 7h14V5H5v2z"/></g></svg>';
 			break;
 		case 'gridicons-reader-share':
 			$svg = '<svg class="gridicon gridicons-reader-share" height="24" width="24" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><g><clipPath id="a"><path d="M0 0h20v20H0z"/></clipPath><g clip-path="url(#a)"><path d="M11.867 6.8V3l6.8 6.65-6.8 6.65v-3.8s-10.2-.884-10.2 4.5c0-10.77 10.2-10.2 10.2-10.2z" stroke="#000" stroke-linecap="round" stroke-width="1.5"/></g></g></svg>';