Fixes #4018

Fixes issue where LastPass' popup window is closed during user attempt
to shift focus from username field to password field.

Auditor: @bridiver

js/components/popupWindow.js

@@ -22,7 +22,7 @@ class PopupWindow extends ImmutableComponent {
   }
 
   onKeyDown (e) {
-    if (e.keyCode === KeyCodes.ESC || e.keyCode === KeyCodes.TAB) {
+    if (e.keyCode === KeyCodes.ESC) {
       windowActions.setPopupWindowDetail()
     }
   }