Unbound-anchor manpage links to non-existent license file

[AlexanderBand]

Describe the bug
Unbound-anchor manpage links to non-existent license file.

To reproduce
Steps to reproduce the behavior:

1. See

   unbound/doc/unbound-anchor.8.in

   Line 162 in 983c716

   http://unbound.nlnetlabs.nl/svn/trunk/LICENSE) and might be stale or

Expected behavior
Link to https://github.com/NLnetLabs/unbound/blob/master/LICENSE