Use Guard::Plugin with updated initialize signature
Fix Notifier to new ::Guard::Notifier interface
Use require instead of autoload

Autoload is deprecated
https://www.ruby-forum.com/topic/3036681
Dummy app: modify $LOAD_PATH

This fixes require from within guard/shotgun
Specify minimum Guard version

Due to incompatibility with previous API
Merge branch 'guard-2' of github.com:jnv/guard-shotgun into jnv-guard-2

Conflicts:
	guard-shotgun.gemspec
	lib/guard/shotgun.rb
Updated Gemfile.lock and dummy app Gemfiles
Merge branch 'jnv-guard-2'