build(deps): update ruby_memcheck requirement from 2.1.2 to 2.2.0

Updates the requirements on [ruby_memcheck](https://github.com/Shopify/ruby_memcheck) to permit the latest version.
- [Release notes](https://github.com/Shopify/ruby_memcheck/releases)
- [Commits](Shopify/ruby_memcheck@2.1.2...2.2.0)

---
updated-dependencies:
- dependency-name: ruby_memcheck
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -8,4 +8,4 @@ gem("rake-compiler-dock", "1.3.0")
 gem("rdoc", "6.5.0")
 gem("psych", "5.1.0")
 
-gem("ruby_memcheck", "2.1.2") if Gem::Platform.local.os == "linux"
+gem("ruby_memcheck", "2.2.0") if Gem::Platform.local.os == "linux"