buildMaven: Check for authenticated attribute

The `authenticated` attribute is not always present in the
`project-info.json` produced by maven2nix[0]

We therefore check for its presence, and default it to false.

[0]: https://github.com/NixOS/mvn2nix-maven-plugin/issues/5#issuecomment-311846950

pkgs/build-support/build-maven.nix

···
   script = writeText "build-maven-repository.sh" ''
     ${lib.concatStrings (map (dep: let
       inherit (dep)
-        url sha1 groupId artifactId version
-        authenticated metadata repository-id;
+        url sha1 groupId artifactId
+        version metadata repository-id;
 
       versionDir = dep.unresolved-version or version;
+      authenticated = dep.authenticated or false;
 
       fetch = (if authenticated then requireFile else fetchurl) {
         inherit url sha1;