chore: Bump minitest from 5.18.0 to 5.18.1

Merge pull request #83 from github/dependabot/bundler/minitest-5.18.1

Author: smockle

Gemfile.lock

@@ -43,7 +43,7 @@ GEM
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
     mini_portile2 (2.8.2)
-    minitest (5.18.0)
+    minitest (5.18.1)
     mocha (2.0.4)
       ruby2_keywords (>= 0.0.5)
     nokogiri (1.15.2)