MDL-57728 theme: Fix text display when using tabs

theme/boost/templates/core/tabtree.mustache

@@ -1,7 +1,41 @@
+{{!
+    This file is part of Moodle - http://moodle.org/
+
+    Moodle is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Moodle is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+}}
+{{!
+    @template core/tabtree
+
+    Tab tree.
+
+    Example context (json):
+    {
+        "tabs": [{
+            "active": "true",
+            "inactive": "false",
+            "link": [{
+                "link": "http://moodle.org"
+            }],
+            "title": "Moodle.org",
+            "text": "Moodle community"
+        }]
+    }
+}}
 <ul class="nav nav-tabs m-b-1">
   {{#tabs}}
     <li class="nav-item">
-      <a class="nav-link {{#active}}active{{/active}} {{#inactive}}disabled{{/inactive}}" {{#link}}href="{{{link}}}"{{/link}} title={{title}}>{{text}}</a>
+      <a class="nav-link {{#active}}active{{/active}} {{#inactive}}disabled{{/inactive}}" {{#link}}href="{{{link}}}"{{/link}} title={{title}}>{{{text}}}</a>
     </li>
   {{/tabs}}
 </ul>