fix: ensure bundle install for pact_broker:dev:setup uses correct Gemfile

Closes: pact-foundation#243

Author: bethesque

tasks/development.rake

@@ -1,10 +1,19 @@
 
+desc 'Set up a dev instance of the Pact Broker'
 task 'pact_broker:dev:setup' do
+  puts "Copying example directory"
   FileUtils.cp_r 'example', 'dev'
   gemfile_contents = File.read('dev/Gemfile')
+
+
+  puts "Changing source of pact_broker gem from rubygems.org to local file system"
   new_gemfile_contents = gemfile_contents.gsub(/^.*gem.*pact_broker.*$/, "gem 'pact_broker', path: '../'")
   File.open('dev/Gemfile', "w") { |file| file << new_gemfile_contents }
-  bundle_install = "BUNDLE_GEMFILE=dev/Gemfile bundle install"
-  puts bundle_install
-  puts `#{bundle_install}`
+
+  Dir.chdir("dev") do
+    Bundler.with_clean_env do
+      puts "Executing bundle install"
+      puts `bundle install`
+    end
+  end
 end