Fixed StateInspector scrollbars on Firefox (#359)

ScrollPane.vue was using "overflow overlay" which is not supported in
Firefox. Changing this to "overflow auto" fixes scrolling
in Firefox while not impacting UI or functionality in Chrome.

Author: Zetaphor

src/devtools/components/ScrollPane.vue

@@ -47,7 +47,7 @@ export default {
 
 .scroll
   flex 1
-  overflow overlay
+  overflow auto
   .app.dark &::-webkit-scrollbar
     background: $dark-background-color
     border-left: 1px solid $dark-border-color