Set text security on line elements only

This ensures the disc does not appear when the field is empty

src/packages/github-sign-in/stylesheets/github-sign-in.less

@@ -1,6 +1,7 @@
 .sign-in-view {
   width: 350px;
   margin-left: -175px;
+
   input, button, .alert {
     margin-bottom: 10px;
   }
@@ -13,7 +14,8 @@
     content: 'Sign in failed. ';
     font-weight: bold;
   }
-  .password {
+
+  .password .line span {
     -webkit-text-security: disc;
   }
 }