Trim content of Import field

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/2380

src/js/3p-filters.js

@@ -368,7 +368,7 @@ const hashFromCurrentFromSettings = function() {
     hash.push(
         listHash.sort().join(),
         qs$('#importLists').checked &&
-            reValidExternalList.test(qs$('#externalLists').value),
+            reValidExternalList.test(qs$('#externalLists').value.trim()),
         qs$('#lists .listEntry.toRemove') !== null
     );
     return hash.join();