vendor: add "v0.8.7" comment to Microsoft/hcsshim vendor

Commit `b3f49c06ffaeef24d09c6c08ec8ec8425a0303e2` was tagged
as `v0.8.7`, so add a comment to the vendor.conf

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor.conf

@@ -1,5 +1,5 @@
 github.com/Azure/go-ansiterm                        d6e3b3328b783f23731bc4d058875b0371ff8109
-github.com/Microsoft/hcsshim                        b3f49c06ffaeef24d09c6c08ec8ec8425a0303e2
+github.com/Microsoft/hcsshim                        b3f49c06ffaeef24d09c6c08ec8ec8425a0303e2 # v0.8.7
 github.com/Microsoft/go-winio                       6c72808b55902eae4c5943626030429ff20f3b63 # v0.4.14
 github.com/docker/libtrust                          9cbd2a1374f46905c68a4eb3694a130610adc62a
 github.com/golang/gddo                              72a348e765d293ed6d1ded7b699591f14d6cd921