rename ocaml_typeconv to type_conv

The actual name of the package is type_conv
(https://github.com/janestreet/type_conv). Having it named
ocaml_typeconv adds a verbosity that isn't required and actually makes
the package harder to find.

pkgs/development/tools/ocaml/oasis/default.nix

@@ -1,4 +1,4 @@
-{stdenv, fetchurl, ocaml, findlib, ocaml_data_notation, ocaml_typeconv, camlp4,
+{stdenv, fetchurl, ocaml, findlib, ocaml_data_notation, type_conv, camlp4,
  ocamlmod, ocamlify, ounit, expect}:
 
 stdenv.mkDerivation {
@@ -13,7 +13,7 @@ stdenv.mkDerivation {
 
   buildInputs =
     [
-      ocaml findlib ocaml_typeconv ocamlmod ocamlify ounit camlp4
+      ocaml findlib type_conv ocamlmod ocamlify ounit camlp4
     ];
 
   propagatedBuildInputs = [ ocaml_data_notation ];