dmgbuild needs to be updated for macOS 11+ compatibility

[carlosperate]

Currently dmgbuild is pinned to version 1.5.2. There is an issue embedding the software license to the dmg (also described in #243), which has been fixed in the v1.6.0 release:

• license adding broken on Big Sur dmgbuild/dmgbuild#29

So, we should update the pup pinned version:

pup/setup.py

Line 39 in 55bf81d

"dmgbuild==1.5.2;sys_platform=='darwin'",