irker: use python3

pkgs/servers/irker/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitLab, python, pkg-config
+{ lib, stdenv, fetchFromGitLab, python3, pkg-config
 , xmlto, docbook2x, docbook_xsl, docbook_xml_dtd_412 }:
 
 stdenv.mkDerivation {
@@ -15,12 +15,14 @@ stdenv.mkDerivation {
   nativeBuildInputs = [ pkg-config xmlto docbook2x docbook_xsl docbook_xml_dtd_412 ];
 
   buildInputs = [
-    python
+    python3
     # Needed for proxy support I believe, which I haven't tested.
     # Probably needs to be propagated and some wrapPython magic
     # python.pkgs.pysocks
   ];
 
+  strictDeps = true;
+
   postPatch = ''
     substituteInPlace Makefile \
       --replace '-o 0 -g 0' ""