Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - Update links to documentation in README.rst

    The links to the docs in README were pointing to Colorodo documentation.

    For master, this should not be pinned to a particular release, but
    should show the most recent docs at all times.

    Change-Id: I3186ea0dbc5105812407a0f87e02d99899a951a0
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>
    (cherry picked from commit 9ea682e950598d39fa53ccabe6c1cd0a4fe426bd)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4f0b229..26938b0 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4f0b2293ce25d8311d352bc4f10708d6a1e00c79
+Subproject commit 26938b0cabc4841e7e75847b728bf7cf54db6aad