Remove bundler installation

It installs bundler without specifying the version in CI.
But, it installs bundler which does not work with old Ruby, and it causes failure.

So, this patch remove bundler installation and uses bundler bundled in Ruby.

Author: Watson1978

.github/workflows/build.yml

@@ -21,7 +21,6 @@ jobs:
           ruby-version: ${{ matrix.ruby }}
       - name: Build and Install
         run: |
-          gem install --no-document bundler
           gem build numo-narray.gemspec
           gem install numo-narray-*.gem
           bundle install
@@ -44,7 +43,6 @@ jobs:
           ruby-version: ${{ matrix.ruby }}
       - name: Build and Install
         run: |
-          gem install --no-document bundler
           gem build numo-narray.gemspec
           gem install numo-narray-*.gem
           bundle install

numo-narray.gemspec

@@ -28,11 +28,6 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.extensions    = ["ext/numo/narray/extconf.rb"]
 
-  if RUBY_VERSION < '2.3' # Ruby 2.2.x
-    spec.add_development_dependency "bundler", "~> 1.3", "< 1.14.0"
-  else
-    spec.add_development_dependency "bundler", ">= 2.2.33"
-  end
   spec.add_development_dependency "rake", ">= 12.3.3"
   spec.add_development_dependency "rake-compiler", "~> 1.1"
   spec.add_development_dependency "test-unit"