add meta verification tag back (#1164)

was removed as I thought it was only used once when you verify the site
but it has to remain in the pages all the time otherwise you get unverified
on Google search console...

Signed-off-by: Nicolas MASSART <nicolas.massart@consensys.net>

custom_theme/main.html

@@ -61,3 +61,7 @@
     </div>
   {% endif %}
 {% endblock %}
+
+{% block extrahead %}
+<meta name="google-site-verification" content="{{config.extra.analytics.verification}}" />
+{% endblock %}

mkdocs.extra.yml

@@ -30,6 +30,7 @@ extra:
   analytics:
     provider: google
     property: 'G-23GVTD3LEQ'
+    verification: 'sGzYdFR_AYDRtsC-SNxMRwjellnfTgs5ZA0q7GIM5j0'
     feedback:
       title: Was this page helpful?
       ratings: