Fix Mjollnir gem build and install

.github/workflows/ubuntu.yml

@@ -42,3 +42,9 @@ jobs:
     - name: Run tests
       run: ~/.rbenv/shims/bundle exec rake test
 
+    - name: Run Mjollnir gem build
+      run: ~/.rbenv/shims/bundle exec rake build
+
+    - name: Run Mjollnir gem install
+      run: ~/.rbenv/shims/bundle exec rake install
+

mjollnir.gemspec

@@ -23,12 +23,15 @@ Gem::Specification.new do |spec|
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
   gemspec = File.basename(__FILE__)
-  spec.files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
+  files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
     ls.readlines("\x0", chomp: true).reject do |f|
       (f == gemspec) ||
         f.start_with?(*%w[bin/ test/ spec/ features/ .git appveyor Gemfile])
     end
   end
+  files << 'ext/mjollnir/parse.c'
+  files << 'ext/mjollnir/parse.h'
+  spec.files = files
   spec.bindir = 'exe'
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']