Some document have non-standard locale code

[ernst77]

Description

Some documents come with style locale as en_GB, en_US this fixes these locale codes

Fixes #

replaces "_" to "-"

Checklist:

• [x ] I have run composer run-script check --timeout=0 and no errors were reported
• [ x] The new code is covered by unit tests (check build/coverage for coverage report)
• I have updated the documentation to describe the changes

[coveralls]

Coverage increased (+0.001%) to 94.634% when pulling 37c15e6 on ErnestStaug:locale_support into 733f845 on PHPOffice:develop.