Update git submodules

* Update docs/submodules/opera from branch 'stable/danube'
  - Add known issue in docs

    Change-Id: Ia02802eeeac10a490dac612348adaf2908347021
    Signed-off-by: Harry Huang <huangxiangyu5@huawei.com>
    (cherry picked from commit 645898cb63b05c96f7fc15aa3934af12d988cd33)

diff --git a/docs/submodules/opera b/docs/submodules/opera
index bcc249f..e86ea37 160000 (submodule)
--- a/docs/submodules/opera
+++ b/docs/submodules/opera
@@ -1 +1 @@
-Subproject commit bcc249f315dca13528dbd100142370b1e97681e3
+Subproject commit e86ea37071b0c8bcf8eaae9c71a40d8b28e760d7