Turn more licenses into lib.licenses style

Should eval cleanly, as far as -A tarball tells me.

Relevant: issue #2999, issue #739

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

@@ -21,6 +21,6 @@ buildPerlPackage rec {
   doCheck = !stdenv.isDarwin;
 
   meta = {
-    license = "perl";
+    license = with stdenv.lib.licenses; [ artistic1 gpl1Plus ];
   };
 }

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 = with stdenv.lib.licenses; [ artistic1 gpl1Plus ];
     platforms = stdenv.lib.platforms.linux;
   };
 }