ci.yml in jekyll-toc-0.15.0.rc

- old
+ new

@@ -1,17 +1,21 @@
 name: CI
-on: [push]
+on: [push, pull_request]
 jobs:
   build:
     strategy:
       matrix:
         ruby: [2.4, 2.5, 2.6, 2.7]
         gemfile:
-        - gemfiles/jekyll_4.0.gemfile
-        - gemfiles/jekyll_3.8.gemfile
+          - gemfiles/jekyll_3.8.gemfile
+          - gemfiles/jekyll_3.9.gemfile
+          - gemfiles/jekyll_4.0.gemfile
+          - gemfiles/jekyll_4.1.gemfile
         exclude:
         - ruby: 2.4
           gemfile: gemfiles/jekyll_4.0.gemfile
+        - ruby: 2.4
+          gemfile: gemfiles/jekyll_4.1.gemfile
     env:
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2