Use plain JS within `clickTab`, make comment more concise

app/assets/javascripts/merge_request_tabs.js.es6

@@ -102,12 +102,18 @@ require('./flash');
     }
 
     clickTab(e) {
-      const targetLink = $(e.target).attr('href');
+      if (e.target) {
+        const targetLink = e.target.getAttribute('href');
+        // Allow following special clicks to make link open in new tab
+        // 1) Cmd + Click on Mac (e.metaKey)
+        // 2) Ctrl + Click on PC (e.ctrlKey)
+        // 3) Middle-click or Mouse Wheel Click (e.which is 2)
         if (e.metaKey || e.ctrlKey || e.which === 2) {
           e.stopImmediatePropagation();
           window.open(targetLink, '_blank');
         }
       }
+    }
 
     tabShown(e) {
       const $target = $(e.target);