[XMonad] Build with ghc 8.6

dotfiles/config/xmonad/src/PagerHints.hs

@@ -31,8 +31,10 @@ xVisibleProp = getAtom "_XMONAD_VISIBLE_WORKSPACES"
 -- | Add support for the \"Current Layout\" and \"Visible Workspaces\" custom
 -- hints to the given config.
 pagerHints :: XConfig a -> XConfig a
-pagerHints c = c { handleEventHook = handleEventHook c +++ pagerHintsEventHook
-           , logHook = logHook c +++ pagerHintsLogHook }
+pagerHints c =
+  c { handleEventHook = handleEventHook c +++ pagerHintsEventHook
+    , logHook = logHook c +++ pagerHintsLogHook
+    }
   where x +++ y = x `mappend` y
 
 -- | Update the current values of both custom hints.

dotfiles/config/xmonad/stack.yaml

@@ -8,7 +8,7 @@ packages:
   extra-dep: true
 extra-deps:
 - X11-xft-0.3.1
-resolver: lts-11.7
+resolver: lts-13.2
 nix:
   packages:
     - pkgconfig
@@ -18,3 +18,4 @@ nix:
     - xorg.libXinerama
     - xorg.libXrandr
     - xorg.libXrender
+    - xorg.libXScrnSaver