Use /usr/bin/env to find perl

This is nicer in nix-shell.

src/script/hydra-create-user

@@ -1,4 +1,4 @@
-#! /var/run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use Hydra::Schema;

src/script/hydra-evaluator

@@ -1,4 +1,4 @@
-#! /run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use utf8;

src/script/hydra-init

@@ -1,4 +1,4 @@
-#! /var/run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use Hydra::Schema;

src/script/hydra-notify

@@ -1,4 +1,4 @@
-#! /run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use utf8;

src/script/hydra-s3-backup-collect-garbage

@@ -1,4 +1,4 @@
-#! /var/run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use File::Basename;

src/script/hydra-send-stats

@@ -1,4 +1,4 @@
-#! /run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use utf8;

src/script/hydra-server

@@ -1,4 +1,4 @@
-#! /var/run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 BEGIN {
     $ENV{CATALYST_SCRIPT_GEN} = 40;

src/script/hydra-update-gc-roots

@@ -1,4 +1,4 @@
-#! /var/run/current-system/sw/bin/perl
+#! /usr/bin/env perl
 
 use strict;
 use File::Path;