chore(firestore): Update minitest to 5.14

refs: googleapis#4110
refs: googleapis#4116

Author: quartzmo

google-cloud-firestore/Gemfile

@@ -9,7 +9,3 @@ gem "google-cloud-errors", path: "../google-cloud-errors"
 gem "rake"
 
 gem "stackprof" unless Gem.win_platform?
-
-# Pin minitest to 5.11.x to avoid warnings emitted by 5.12.
-# See https://github.com/googleapis/google-cloud-ruby/issues/4110
-gem "minitest", "~> 5.11.3"

google-cloud-firestore/google-cloud-firestore.gemspec

@@ -27,7 +27,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency "rbtree", "~> 0.4.2"
 
   gem.add_development_dependency "google-style", "~> 1.24.0"
-  gem.add_development_dependency "minitest", "~> 5.10"
+  gem.add_development_dependency "minitest", "~> 5.14"
   gem.add_development_dependency "minitest-autotest", "~> 1.0"
   gem.add_development_dependency "minitest-focus", "~> 1.1"
   gem.add_development_dependency "minitest-rg", "~> 5.2"