mysql deprecation

Line 4383 (wpgmaps_filter()) uses mysql_real_escape_string which is no longer required to be available as of WordPress 3.9 and discouraged/ deprecated as of PHP 5.5.
Not sure where or if the function wpgmaps_filter() is called.

Should rather use esc_sql() or $wpdb for escaping.

https://ww.wp.xz.cn/plugins/wp-google-maps/