Update git submodules

* Update docs/submodules/qtip from branch 'master'
  - Merge "Use pipenv instead of pip"
  - Use pipenv instead of pip

    pipenv[1] is the officially recommended Python packaging tool from Python.org[2]

    [1]: https://docs.pipenv.org/
    [2]: https://packaging.python.org/new-tutorials/installing-and-using-packages/

    It integrates pip with virtualenv and handles version management better than pip.

    Change-Id: I4ec6436e29d76a866b56caa609e2bcd22489ae9f
    Signed-off-by: Yujun Zhang <zhang.yujunz@zte.com.cn>

diff --git a/docs/submodules/qtip b/docs/submodules/qtip
index 4daf798..33fe72d 160000 (submodule)
--- a/docs/submodules/qtip
+++ b/docs/submodules/qtip
@@ -1 +1 @@
-Subproject commit 4daf79855c2dccff22134939245497140343bfa3
+Subproject commit 33fe72d9e48315fc79cec9610ebfb81f5cb6047d