Use ghc 8.10.6 in nix build

Update nix build script and github workflow configuration to use ghc 8.10.6
instead of 8.10.4.

.github/workflows/ci.yml

@@ -225,7 +225,7 @@ jobs:
           # - nixpkgs: "channel:nixos-20.09"
           #   compiler: "ghc884"
           - nixpkgs: "channel:nixos-unstable"
-            compiler: "ghc8104"
+            compiler: "ghc8106"
           # - nixpkgs: "channel:nixos-unstable"
           #   compiler: "ghc901"
 
@@ -245,13 +245,13 @@ jobs:
         run: nix-build --argstr compiler ${{ matrix.compiler }}
 
       - name: Build container image stream
-        if: matrix.compiler == 'ghc8104' && github.ref == 'refs/heads/master'
+        if: matrix.compiler == 'ghc8106' && github.ref == 'refs/heads/master'
         run: |
           nix-build --argstr compiler ${{ matrix.compiler }} ./nix/docker.nix
           echo "image_stream=$(readlink result)" >> $GITHUB_ENV
 
       - name: Push image to ghcr.io
-        if: matrix.compiler == 'ghc8104' && github.ref == 'refs/heads/master'
+        if: matrix.compiler == 'ghc8106' && github.ref == 'refs/heads/master'
         env:
           CRED: ${{ secrets.GHCR_USER }}:${{ secrets.GHCR_PAT }}
           FROM: docker-archive:/dev/stdin

default.nix

@@ -1,6 +1,6 @@
 {
   nixpkgs ? <nixpkgs>,
-  compiler ? "ghc8104"
+  compiler ? "ghc8106"
 }:
 
 let