Update git submodules

* Update storlets from branch 'master'
  to b4e005a80d3bfd988bc7ce08961f0587c42f3621
  - Update supported python versions

    ... according to the versions currently tested.

    Python 3.6 support is removed because it was removed from swift by
    0714557aa8ea312dd38ff8df0eff925ca3d829e8 .

    Change-Id: I5db0dc1fa86cc78e7d8a6bfde19e76f2d9dc65a5
    Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

diff --git a/storlets b/storlets
index cb615e59418bbe24f6c32b6d2f54e2e6e2ae4d3c..b4e005a80d3bfd988bc7ce08961f0587c42f3621 160000 (submodule)
--- a/storlets
+++ b/storlets
@@ -1 +1 @@
-Subproject commit cb615e59418bbe24f6c32b6d2f54e2e6e2ae4d3c
+Subproject commit b4e005a80d3bfd988bc7ce08961f0587c42f3621