Update dependency json to "< 2.15.3"

Author: renovate[bot]

Gemfile

@@ -5,5 +5,5 @@ gemspec :name => "brakeman"
 unless ENV['BM_PACKAGE']
   gem "rake", "< 13.2.2"
   gem "codeclimate-test-reporter", group: :test, require: nil
-  gem "json", "< 2.15.1", group: :test, require: nil # For Ruby 1.9.3 https://github.com/colszowka/simplecov/issues/511
+  gem "json", "< 2.15.3", group: :test, require: nil # For Ruby 1.9.3 https://github.com/colszowka/simplecov/issues/511
 end