Fixed change task to work with newlines

Related: #1534

There are several problems with the code, one of them is an ugly hack to work around nils while detecting new lines: https://github.com/arr-ee/leiningen/compare/technomancy:master...arr-ee:fix-1534?expand=1#diff-21e63a7dce468cc21647ec25185b627bR73
I’ve tried to clean it up, but gave up for a while.

There are two failing tests that are left from the current master. They do not include newlines (i.e. project definition is a one-liner), so I’m not sure it’s worth it to try and fix those.