The exported version env var should have a consistent length

Summary:
Prepend a 0 to the VERSION_MICRO part of the KONSOLE_VERSION string
to make the env var length consistent, so that conditions that depend
on it actually work.

For example, the second version should be higher than the first one:
  18.04.12 -> 180412
  18.08.1  -> 180801

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D12733