allow digits in event names

[mwr]

At the moment it is not allowed to have event names containing digits, though this was possible in Magento1.
For example a event name like mwltr83_my_event is not allowed within the events.xsd.

Description

This pull requests updates the events.xsd and adds 0-9 to allowed values in the regex.

Fixed Issues (if relevant)

void

Manual testing scenarios

void

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[miguelbalparda]

Hi @mwr! Checking this it seems this change does not have any backward compatibility issue but I will double check internally and report back. Thanks for your contribution!

[fooman]

I am guessing this should bump the feature (minor) version of the framework package to allow for targeting of this feature of the xsd validation as "mwltr83_my_event" would validate on 2.2.1 (if it's included in the next release) but would fail for 2.2.0.