build(deps): update rake-compiler-dock requirement from 1.3.0 to 1.3.1

Updates the requirements on [rake-compiler-dock](https://github.com/rake-compiler/rake-compiler-dock) to permit the latest version.
- [Release notes](https://github.com/rake-compiler/rake-compiler-dock/releases)
- [Changelog](https://github.com/rake-compiler/rake-compiler-dock/blob/master/History.md)
- [Commits](rake-compiler/rake-compiler-dock@1.3.0...1.3.1)

---
updated-dependencies:
- dependency-name: rake-compiler-dock
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile

@@ -4,7 +4,7 @@ gemspec
 
 gem("minitest", "5.20.0")
 gem("rake-compiler", "1.2.5")
-gem("rake-compiler-dock", "1.3.0")
+gem("rake-compiler-dock", "1.3.1")
 gem("rdoc", "6.5.0")
 gem("psych", "5.1.0")