containerd: fix --version output

Before this change, 'containerd --version' with the nix package wouldn't
print useful version information.

In addition, the build output a bunch of (harmless) errors about 'git:
command not found'.

This fixes both of those problems.

pkgs/applications/virtualization/containerd/default.nix

@@ -5,6 +5,8 @@ with lib;
 buildGoPackage rec {
   pname = "containerd";
   version = "1.2.13";
+  # git commit for the above version's tag
+  commit = "7ad184331fa3e55e52b890ea95e65ba581ae3429";
 
   src = fetchFromGitHub {
     owner = "containerd";
@@ -20,7 +22,7 @@ buildGoPackage rec {
 
   buildInputs = [ btrfs-progs ];
 
-  buildFlags = [ "VERSION=v${version}" ];
+  buildFlags = [ "VERSION=v${version}" "REVISION=${commit}" ];
 
   BUILDTAGS = []
     ++ optional (btrfs-progs == null) "no_btrfs";
@@ -28,7 +30,7 @@ buildGoPackage rec {
   buildPhase = ''
     cd go/src/${goPackagePath}
     patchShebangs .
-    make binaries
+    make binaries $buildFlags
   '';
 
   installPhase = ''