fixed driftcorrect bug when calculating single value corrections/updateed changelog

maybe not hot, but fix.

changed milestone to %2.1.0

added BUG label

requested review from @schaefed

mentioned in issue #331 (closed)

approved this merge request

Apart from the ongoing discussion in #331 (closed) this LGTM and fixes the most urgent issue.

merged

mentioned in commit f1bcf777

mentioned in commit 63b55c6d

mentioned in commit 684dc8a0

mentioned in commit 8f7a90e4