fixes typo in variable name that prevents theme installation

create.sh

@@ -64,7 +64,7 @@ docker exec --user www-data $DOCKER_PREFIX-web /bin/sh -c "
 
 echo "Installing WordPress $WP_THEME theme";
 docker exec --user www-data $DOCKER_PREFIX-web /bin/sh -c "
-    wp theme install $THEME \
+    wp theme install $WP_THEME \
         --activate \
         --path=/var/www/html";