Bump minitest to 5.11.3 to match Gitaly version

This prevents us from shipping duplicate versions of this gem.

Gemfile

@@ -337,7 +337,7 @@ group :development, :test do
   gem 'rspec-parameterized', require: false
 
   # Prevent occasions where minitest is not bundled in packaged versions of ruby (see #3826)
-  gem 'minitest', '~> 5.7.0'
+  gem 'minitest', '~> 5.11.0'
 
   # Generate Fake data
   gem 'ffaker', '~> 2.10'

Gemfile.lock

@@ -463,7 +463,7 @@ GEM
     mini_magick (4.8.0)
     mini_mime (1.0.1)
     mini_portile2 (2.3.0)
-    minitest (5.7.0)
+    minitest (5.11.3)
     msgpack (1.2.4)
     multi_json (1.13.1)
     multi_xml (0.6.0)
@@ -1054,7 +1054,7 @@ DEPENDENCIES
   method_source (~> 0.8)
   mimemagic (~> 0.3.2)
   mini_magick
-  minitest (~> 5.7.0)
+  minitest (~> 5.11.0)
   mysql2 (~> 0.4.10)
   nakayoshi_fork (~> 0.0.4)
   net-ldap