puppet_webhook is not compatible with Ruby < 2.2.2

[dhollinger]

When attempting to install puppet_webhook on Ruby < 2.2.2, it will error out with the following error:

ERROR:  Error installing puppet_webhook:
	rack requires Ruby version >= 2.2.2.

This has potential impact to any puppet_webhook user that uses Puppet < 5.0.0. We either need to update the gemspec and code to make it compatible with Sinatra < 2.x or remove information listing compatibility with Ruby < 2.2.2

[bastelfreak]

I am fine with dropping puppet 4. This is a nee project and puppet 4 is EOL in the end of this year anyways.

[dhollinger]

Solved by #58