Bump octokit requirement to ~> 4.18, which is compatible with faraday 1

See github/pages-gem#665

Author: mokagio

Gemfile.lock

@@ -8,7 +8,7 @@ PATH
       git (~> 1.3)
       jsonlint
       nokogiri (>= 1.10.4)
-      octokit (~> 4.13)
+      octokit (~> 4.18)
       parallel (~> 1.14)
       progress_bar (~> 1.3)
       rake (~> 12.3)

fastlane-plugin-wpmreleasetoolkit.gemspec

@@ -35,7 +35,7 @@ Gem::Specification.new do |spec|
   # spec.add_dependency 'your-dependency', '~> 1.0.0'
   spec.add_dependency 'diffy', '~> 3.3'
   spec.add_dependency 'nokogiri', '>= 1.10.4'
-  spec.add_dependency 'octokit', '~> 4.13'
+  spec.add_dependency 'octokit', '~> 4.18'
   spec.add_dependency 'git', '~> 1.3'
   spec.add_dependency 'jsonlint'
   spec.add_dependency('rake', '~> 12.3')