chore(isMailtoURI): remove unnecessary default to (#2341)

* chore: add additional testcases to isMailtoURI

Line 44 is only partially covered before this change

* chore: add additonal const to figure out which part is partial

* chore: add testcase for single ?

* chore: add another line to find partial coverage

* chore: remove default to

* chore: combine consts again

src/lib/isMailtoURI.js

@@ -41,7 +41,7 @@ export default function isMailtoURI(url, options) {
     return false;
   }
 
-  const [to = '', queryString = ''] = url.replace('mailto:', '').split('?');
+  const [to, queryString = ''] = url.replace('mailto:', '').split('?');
 
   if (!to && !queryString) {
     return true;