fix typo: 'mailto:' protocol not 'mailto'

Author: etpinard

src/lib/svg_text_utils.js

@@ -221,7 +221,7 @@ var TAG_STYLES = {
     em: 'font-style:italic;font-weight:bold'
 };
 
-var PROTOCOLS = ['http:', 'https:', 'mailto'];
+var PROTOCOLS = ['http:', 'https:', 'mailto:'];
 
 var STRIP_TAGS = new RegExp('</?(' + Object.keys(TAG_STYLES).join('|') + ')( [^>]*)?/?>', 'g');