Flow bugfix release: 8.1.13

Unfortunately there was a bug in the previous 8.1.12 release which included incompatible code from higher versions.
I am sorry if this created inconvenience in your installations.
Note that 8.1.13 is back to the state 8.1.11 was in, so hopefully you did not try to adjust your codebase to these “breaking changes” (that wrongly went into 8.1.12).