Add SVG mime support

[gregrickaby]

This needs to go into hooks.php

/**
 * Enable custom mime types.
 *
 * @param array $mimes Current allowed mime types.
 * @return array                Updated allowed mime types.
 */
function _s_custom_mime_types( $mimes ) {
	$mimes['svg'] = 'image/svg+xml';
	$mimes['svgz'] = 'image/svg+xml';
	return $mimes;
}
add_filter( 'upload_mimes', '_s_custom_mime_types' );