BC break in 4.6.3

A BC Break has been introduced in a patch version.

https://github.com/vimeo/psalm/commit/205fdd197e914a5377053f9378a7112236a83b50#diff-58b56f2d1a81b22decaddcb6bce7b755662ebf12b8e17e20fd60dc5809787c99

Plugins relying on IssueBuffer::finish are now failing.
https://github.com/Roave/you-are-using-it-wrong/issues/114
