Temporarily symlink stack.yaml to stack-master.yaml

This shall be reverted together with the .github/workflows/stack.yml
part of 229d52ff07 once xmonad 0.17 is
out.

stack-master.yaml

@@ -1,7 +1,7 @@
 # This stack.yaml is used to build xmonad-contrib with master version
 # of xmonad
 
-resolver: lts-15.3
+resolver: lts-17.14
 
 packages:
 - ./
@@ -12,5 +12,15 @@ extra-deps:
 - github: xmonad/xmonad
   commit: master@{today}
 
+nix:
+  packages:
+    - pkg-config
+    - xorg.libX11
+    - xorg.libXext
+    - xorg.libXft
+    - xorg.libXrandr
+    - xorg.libXrender
+    - xorg.libXScrnSaver
+
 ghc-options:
   xmonad-contrib: '-j'