Bug#1020046: slimit: FTBFS: ModuleNotFoundError: No module named 'minifier'

[Bastian Germann]

This needs to be converted to a relative import.
Upstream did this in commit 
https://github.com/rspivak/slimit/commit/40956e7fc6e954b3e6d7b629faeb3303f5efb7ea