BUG: Fix for Sphinx 3.4+ search (#213)

Our version of readthedocs/sphinx_rtd_theme#1021 to fix issues due to sphinx-doc/sphinx#8623, i.e., `search.html` not actually searching due to `Uncaught ReferenceError: Stemmer is not defined` in Sphinx 3.4+.

Closes #214 
Closes #220

sphinx_bootstrap_theme/bootstrap/search.html

@@ -10,8 +10,9 @@
 {%- extends "layout.html" %}
 {% set title = _('Search') %}
 {% block extrahead %}
-  <script type="text/javascript" src="{{ pathto('_static/searchtools.js', 1) }} "></script>
-  <script type="text/javascript" src="{{ pathto('searchindex.js', 1) }} "></script>
+  <script type="text/javascript" src="{{ pathto('_static/searchtools.js', 1) }}"></script>
+  <script type="text/javascript" src="{{ pathto('_static/language_data.js', 1) }}"></script>
+  <script type="text/javascript" src="{{ pathto('searchindex.js', 1) }}"></script>
   {# this is used when loading the search index using $.ajax fails,
      such as on Chrome for documents on localhost #}
   <script type="text/javascript" id="searchindexloader"></script>