[commit: ghc] ghc-8.6's head updated: circleci: Reduce compression effort to 3 (e734b8c)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

Branch 'ghc-8.6' now includes:

     6826815 Bump Cabal submodule
     6328e89 Allow arbitrary options to be passed to tar compression
     d414a11 circleci: Fix documentation building
     1741e85 circleci: Reduce build verbosity
     e734b8c circleci: Reduce compression effort to 3