Merge pull request #44 from ruby-syntax-tree/dependabot/bundler/minitest-5.21.1

Bump minitest from 5.20.0 to 5.21.1

Author: github-actions[bot]

Gemfile.lock

@@ -9,7 +9,7 @@ GEM
   remote: https://rubygems.org/
   specs:
     docile (1.4.0)
-    minitest (5.20.0)
+    minitest (5.21.1)
     prettier_print (1.2.1)
     rake (13.1.0)
     simplecov (0.22.0)