Log Message:
Update ruby-prawn to 2.2.2.

2.2.0

Notable changes:

* Added support for TTC fonts
* Added Join style validation
* Fixed handling of NBSP in Windows-1252 text
* Fixed wrong leading of one-line paragraphs
* Fixed dashing
* Added Code of Conduct
* Improved generated document consistency
* Improved gradients
* Supported Rubies have
* Added unexpected manual changes signaling
* Added colors validation
* Fixed CannotFit for zero-width spaces