Convert imports to ES6 from CommonJS

This is needed because `require()` means something different in webpack - it ends up importing the module as something we didn't expect (and is occasionally async)

src/autocomplete/UserProvider.js

@@ -91,7 +91,7 @@ export default class UserProvider extends AutocompleteProvider {
         this.users = null;
     }
 
-    async getCompletions(query: string, selection: SelectionRange, force?: boolean = false): Array<Completion> {
+    async getCompletions(query: string, selection: SelectionRange, force: boolean = false): Array<Completion> {
         const MemberAvatar = sdk.getComponent('views.avatars.MemberAvatar');
 
         // lazy-load user list into matcher