Bump max_input_vars to 1800 for Avada Wordpress theme

Avada wants 1660 it seems

Dockerfile

@@ -42,6 +42,7 @@ RUN echo "Listen 8000" > /etc/apache2/ports.conf
 RUN a2enmod rewrite
 RUN crudini --set /etc/php/7.0/apache2/php.ini PHP upload_max_filesize 500M && \
     crudini --set /etc/php/7.0/apache2/php.ini PHP post_max_size 500M && \
+    crudini --set /etc/php/7.0/apache2/php.ini PHP max_input_vars 1800 && \
     crudini --set /etc/php/7.0/apache2/php.ini Session session.save_path /run/wordpress/sessions
 
 ADD start.sh /app/code/start.sh