Per https://groups.google.com/d/msg/bazel-discuss/dO2MHQLwJF0/2OXHjMAaAAAJ the native rules for http_archive
are to be replaced with their skylark implementations. This commit updates the WORKSPACE to use the skylark
definitions.

Tested using `bazel build //... --incompatible_remove_native_http_archive --incompatible_remove_native_git_repository`