Update git submodules

* Update docs/submodules/ipv6 from branch 'stable/danube'
  - Fix typo issue

    Change-Id: If4d0bad9d2ce0e90dd59f11a4bec7484307feacc
    Signed-off-by: Bin Hu <bh526r@att.com>
    (cherry picked from commit 087c95c300b0c6599a1c9d39151d06df1352789c)

  - Final 1.0.0 for Release Notes

    Change-Id: I2494a6c28233d6667ebab5db97c7366a1762f817
    Signed-off-by: Bin Hu <bh526r@att.com>
    (cherry picked from commit 4ee9deb73423eafc67f37c076fc7e2de9535efd2)

  - Split Gap Analysis into 2 files

    One for OpenStack Newton, and the other for ODL Boron.

    Change-Id: Ic2e7d67c44e33009a402e02ea27d9c0fe38485ef
    Signed-off-by: Bin Hu <bh526r@att.com>
    (cherry picked from commit 951f066001be8a3184084a759f3a9ef4d2fcfa20)

  - Update the reference URL of OPNFV Releases

    Change-Id: I010074952edb8f5ef100cd48414c8cc6f518a76b
    Signed-off-by: Bin Hu <bh526r@att.com>
    (cherry picked from commit e136eed871db256c4ffbcd21eb0eeef1e2735d7a)

  - Draft of Release Notes

    Change-Id: I76d4390f3916bb9eff14ef477e6274d47d501d67
    Signed-off-by: Bin Hu <bh526r@att.com>
    (cherry picked from commit 6805a791acbbaa26d3363dc8dabcdff4c7a1d99a)

diff --git a/docs/submodules/ipv6 b/docs/submodules/ipv6
index b0f5f1e..a6fe8cb 160000 (submodule)
--- a/docs/submodules/ipv6
+++ b/docs/submodules/ipv6
@@ -1 +1 @@
-Subproject commit b0f5f1eaad58121464b25169e04a7191a0ad34f4
+Subproject commit a6fe8cb94cbfa56134baa43d872f15f79bc16e6b