Bump git from 1.8.1 to 1.13.1

Bumps [git](https://github.com/ruby-git/ruby-git) from 1.8.1 to 1.13.1.
- [Release notes](https://github.com/ruby-git/ruby-git/releases)
- [Changelog](https://github.com/ruby-git/ruby-git/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ruby-git/ruby-git/compare/v1.8.1...v1.13.1)

---
updated-dependencies:
- dependency-name: git
  dependency-type: indirect
...

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

Gemfile.lock

@@ -39,7 +39,8 @@ GEM
       faraday (>= 0.8)
     faraday-net_http (1.0.1)
     faraday-net_http_persistent (1.1.0)
-    git (1.8.1)
+    git (1.13.1)
+      addressable (~> 2.8)
       rchardet (~> 1.8)
     kramdown (2.3.1)
       rexml