fix(modal): make scrolling on iOS Safari work

This fixes a bug where the full-screen modal would not work on iOS Safari (and only there). It's unclear why this is happening due to a single overflow: visible statement though.

Resolves https://github.com/go-vikunja/vikunja/issues/325

(cherry picked from commit 16d7386975)

frontend/src/components/misc/Modal.vue

@@ -219,7 +219,6 @@ $modal-width: 1024px;
 
   .modal-container {
     height: auto;
-    overflow: visible;
 	min-height: 100vh;
   }