Update zlib URL in r0.10 branch (#6951)

Fixed #6950
diff --git a/tensorflow/workspace.bzl b/tensorflow/workspace.bzl
index d917562..a72f36e 100644
--- a/tensorflow/workspace.bzl
+++ b/tensorflow/workspace.bzl
@@ -198,7 +198,7 @@
 
   native.new_http_archive(
     name = "zlib_archive",
-    url = "http://zlib.net/zlib-1.2.8.tar.gz",
+    url = "http://zlib.net/fossils/zlib-1.2.8.tar.gz",
     sha256 = "36658cb768a54c1d4dec43c3116c27ed893e88b02ecfcb44f2166f9c0b7f2a0d",
     build_file = path_prefix + "zlib.BUILD",
   )