[Chore] Bump to rc-4

CHANGELOG.md

@@ -1,6 +1,6 @@
 # GooseMod Changelog
 
-## v12.1-dev [2021-09-15]
+## v12.1-dev [2021-09-17]
 
   - ### Store
     - **Ludicrous speed.** The Store should now be quite faster, especially on low-end hardware.

src/index.js

@@ -108,7 +108,7 @@ const init = async function () {
   }
 
   this.versioning = {
-    version: `12.1-dev (rc-3)`,
+    version: `12.1-dev (rc-4)`,
     hash: '<hash>', // Hash of built final js file is inserted here via build script
 
     lastUsedVersion: this.storage.get('goosemodLastVersion')