Fix rubocop-rake warning

``` The following RuboCop extension libraries are installed but not loaded in config: * rubocop-rake ```
premailer · Apr 7, 2024 · b41be39 · b41be39
1 parent e321967
commit b41be39
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/.rubocop.yml b/.rubocop.yml
@@ -1,3 +1,6 @@
+require:
+  - rubocop-rake
+
 AllCops:
   TargetRubyVersion: 2.7  # lowest supported version
   NewCops: enable