Update git requirement from = 1.2.9 to = 1.18.0

Updates the requirements on [git](https://github.com/ruby-git/ruby-git) to permit the latest version.
- [Release notes](https://github.com/ruby-git/ruby-git/releases)
- [Changelog](https://github.com/ruby-git/ruby-git/blob/master/CHANGELOG.md)
- [Commits](ruby-git/ruby-git@v1.2.9...v1.18.0)

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

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

Gemfile.lock

@@ -2,12 +2,14 @@ PATH
   remote: .
   specs:
     redbutton (0.0.10)
-      git (= 1.2.9)
+      git (= 1.18.0)
       gli (= 2.12.2)
 
 GEM
   remote: https://rubygems.org/
   specs:
+    addressable (2.8.4)
+      public_suffix (>= 2.0.2, < 6.0)
     aruba (0.14.1)
       childprocess (~> 0.5.6)
       contracts (~> 0.9)
@@ -33,12 +35,16 @@ GEM
     diff-lcs (1.2.5)
     ffi (1.9.14)
     gherkin (4.0.0)
-    git (1.2.9)
+    git (1.18.0)
+      addressable (~> 2.8)
+      rchardet (~> 1.8)
     gli (2.12.2)
     json (1.8.3)
     multi_json (1.12.1)
     multi_test (0.1.2)
+    public_suffix (5.0.1)
     rake (11.2.2)
+    rchardet (1.8.0)
     rdoc (4.2.2)
       json (~> 1.4)
     rspec (3.5.0)

redbutton.gemspec

@@ -21,5 +21,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency('aruba')
   s.add_development_dependency('rspec')
   s.add_runtime_dependency('gli','2.12.2')
-  s.add_runtime_dependency('git','1.2.9')
+  s.add_runtime_dependency('git','1.18.0')
 end