DEV: Run rubocop in parallel in pre-commit hook.

DEV: Run rubocop in parallel in pre-commit hook.

diff --git a/lefthook.yml b/lefthook.yml
index 749f080..f3645c3 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -3,7 +3,7 @@ pre-commit:
   commands:
     rubocop:
       glob: "*.rb"
-      run: bundle exec rubocop {staged_files}
+      run: bundle exec rubocop --parallel {staged_files}
     prettier:
       glob: "*.{js,es6}"
       exclude: "vendor/*|fixtures|public/javascripts|shims.js|ember-addons|template-lintrc|locale/*|test_helper|run-qunit"

GitHub sha: 960fd947