mkpasswd: Fix complaining about missing pkg-config

Before, when building, would output multiple times:

> sh: line 1: pkg-config: command not found

1 files changed, 2 insertions, 2 deletions

diff --git a/pkgs/tools/security/mkpasswd/default.nix b/pkgs/tools/security/mkpasswd/default.nix
index e001239f3136e..c884c27900063 100644
--- a/pkgs/tools/security/mkpasswd/default.nix
+++ b/pkgs/tools/security/mkpasswd/default.nix
@@ -1,11 +1,11 @@
-{ lib, stdenv, whois, perl }:
+{ lib, stdenv, whois, perl, pkg-config }:
 
 stdenv.mkDerivation {
   name = "mkpasswd-${whois.version}";
 
   src = whois.src;
 
-  nativeBuildInputs = [ perl ];
+  nativeBuildInputs = [ perl pkg-config ];
 
   preConfigure = whois.preConfigure;
   buildPhase = "make mkpasswd";