Turn some license strings into lib.licenses values

pkgs/development/perl-modules/Compress-Raw-Zlib/default.nix

@@ -21,6 +21,6 @@ buildPerlPackage rec {
   doCheck = !stdenv.isDarwin;
 
   meta = {
-    license = "perl5";
+    license = stdenv.lib.licenses.perl5;
   };
 }

pkgs/development/perl-modules/DBD-Pg/default.nix

@@ -16,7 +16,7 @@ buildPerlPackage rec {
   meta = {
     homepage = http://search.cpan.org/dist/DBD-Pg/;
     description = "DBI PostgreSQL interface";
-    license = "perl";
+    license = stdenv.lib.licenses.perl5;
     platforms = stdenv.lib.platforms.linux;
   };
 }

pkgs/development/perl-modules/maatkit/default.nix

@@ -34,7 +34,7 @@ buildPerlPackage rec {
       In addition to MySQL, there is support for PostgreSQL, Memcached, and a
       growing variety of other databases and technologies.
     '';
-    license = "GPLv2+";
+    license = stdenv.lib.licenses.gpl2Plus;
     homepage = http://www.maatkit.org/;
   };
 }