linuxPackages: 4.14 -> 4.19

This reverts commit 048c36c.

With the patch applied for fixing the overlayfs bug in QEMU, there
really shouldn't stand anything in our way to use 4.19 as the default
kernel.

Signed-off-by: aszlig <aszlig@nix.build>

pkgs/top-level/all-packages.nix

@@ -14891,7 +14891,7 @@ in
   });
 
   # The current default kernel / kernel modules.
-  linuxPackages = linuxPackages_4_14;
+  linuxPackages = linuxPackages_4_19;
   linux = linuxPackages.kernel;
 
   # Update this when adding the newest kernel major version!