Revert "GHC 8.4 is out"

This reverts commit 847dffe.

Author: ndmitchell

.travis.yml

@@ -7,7 +7,7 @@ matrix:
   - env: GHCVER=7.10.3
   - env: GHCVER=8.0.2
   - env: GHCVER=8.2.2
-  - env: GHCVER=8.4.4
+  - env: GHCVER=8.4.3
   - env: GHCVER=8.6.1
   - env: GHCVER=head
   - os: osx

shake.cabal

@@ -30,7 +30,7 @@ description:
     (e.g. compiler version).
 homepage:           https://shakebuild.com
 bug-reports:        https://github.com/ndmitchell/shake/issues
-tested-with:        GHC==8.6.1, GHC==8.4.4, GHC==8.2.2, GHC==8.0.2, GHC==7.10.3, GHC==7.8.4, GHC==7.6.3, GHC==7.4.2
+tested-with:        GHC==8.6.1, GHC==8.4.3, GHC==8.2.2, GHC==8.0.2, GHC==7.10.3, GHC==7.8.4, GHC==7.6.3, GHC==7.4.2
 extra-doc-files:
     CHANGES.txt
     README.md