Switch shortcodes should match uppercase variables

When using `[switch field="package" Gold="something gold specific" ... ]` (Note the capital **G** in *Gold*) it won't match upercase letters in the URI, but will match lowercase.

WordPress passes arguments through `shortcode_parse_atts($text)` which does a `strtolower($m[1])` on the attributes. I doubt its possible to make it case sensitive matching, but the code should be modified to run the URI through `strtolower` to at least allow case insensitive matching.

See the WordPress file [here](https://github.com/WordPress/WordPress/blob/master/wp-includes/shortcodes.php#L292)