fix(database): Add missing "typeof" (#74)

https://github.com/firebase/firebase-js-sdk/blob/fd0728138d88c454f8e38a78f35d831d6365070c/src/database/js-client/core/Repo.js#L86

Author: jsayol

src/database/core/Repo.ts

@@ -84,7 +84,7 @@ export class Repo {
       const authOverride = app.options['databaseAuthVariableOverride'];
       // Validate authOverride
       if (typeof authOverride !== 'undefined' && authOverride !== null) {
-        if (authOverride !== 'object') {
+        if (typeof authOverride !== 'object') {
           throw new Error('Only objects are supported for option databaseAuthVariableOverride');
         }
         try {