batik: mark as insecure

The package hasn't been updated in a long time. There have been several
issues with the package. There is no dependant  package in the
repository so marking it as insecure until someone maintains it sounds
reasonable.

pkgs/applications/graphics/batik/default.nix

@@ -15,5 +15,11 @@ stdenv.mkDerivation {
     homepage = https://xmlgraphics.apache.org/batik;
     license = licenses.asl20;
     platforms = platforms.unix;
+    knownVulnerabilities = [
+      # vulnerabilities as of 16th October 2018 from https://xmlgraphics.apache.org/security.html:
+      "CVE-2018-8013"
+      "CVE-2017-5662"
+      "CVE-2015-0250"
+    ];
   };
 }