Remove dependency on ActiveSupport strip_heredoc

Instead we can use features of modern Ruby - the squiggly heredoc (<<~).
Which also means we no longer need ActiveSupport 🎉

Author: stevenharman

git_tracker.gemspec

@@ -32,11 +32,6 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.platform = Gem::Platform::RUBY
 
-  if RUBY_VERSION >= "2.5.0"
-    spec.add_development_dependency "activesupport", "~> 6.0"
-  else
-    spec.add_development_dependency "activesupport", "~> 5.0"
-  end
   spec.add_development_dependency "pry-byebug", "~> 3.9"
   spec.add_development_dependency "rake", "~> 13.0"
   spec.add_development_dependency "rspec", "~> 3.9"

spec/git_tracker/commit_message_spec.rb

@@ -1,5 +1,4 @@
 require "git_tracker/commit_message"
-require "active_support/core_ext/string/strip"
 
 RSpec.describe GitTracker::CommitMessage do
   include CommitMessageHelper
@@ -90,15 +89,17 @@ def stub_commit_message(story_text)
 
   describe "#append" do
     let(:fake_file) { GitTracker::FakeFile.new }
+
     before do
       allow(File).to receive(:open).and_yield(fake_file)
     end
+
     def stub_original_commit_message(message)
       allow(File).to receive(:read) { message }
     end
 
     it "handles no existing message" do
-      commit_message_text = <<-COMMIT_MESSAGE.strip_heredoc
+      commit_message_text = <<~COMMIT_MESSAGE
 
 
         [#8675309]
@@ -112,7 +113,7 @@ def stub_original_commit_message(message)
     end
 
     it "preserves existing messages" do
-      commit_message_text = <<-COMMIT_MESSAGE.strip_heredoc
+      commit_message_text = <<~COMMIT_MESSAGE
         A first line
 
         With more here
@@ -128,7 +129,7 @@ def stub_original_commit_message(message)
     end
 
     it "preserves line breaks in comments" do
-      commit_message_text = <<-COMMIT_MESSAGE.strip_heredoc
+      commit_message_text = <<~COMMIT_MESSAGE
 
 
         [#8675309]