Unable to release if change log contains 'Ù'

[johlju]

If the change log contains ÙTF-8 instead of UTF-8 the GitHub release fails with the error

ERROR: {"message":"Problems parsing JSON","documentation_url":"https://developer.github.com/v3/repos/releases/#create-a-release"}
At /Users/johlju/source/xFailOverCluster/output/RequiredModules/Sampler/0.99.0/tasks/GitHubRelease.functions.ps1:71 char:17

We should remove any invalid characters here, or throw an error saying that invalid characters was detected, and have the changelog HQRM QA test check for this.

https://github.com/gaelcolas/Sampler/blob/dee451c8ce1f925d36e344aa663624618d811e4e/.build/tasks/GitHubRelease.functions.ps1#L64