Update ONOS docker image to the latest 1.8.1-SNAPSHOT

Change-Id: I7e2bd7153cf1912c38b63bf9346a964b68e69e8c
diff --git a/build.gradle b/build.gradle
index f29afa3..585331c 100644
--- a/build.gradle
+++ b/build.gradle
@@ -90,7 +90,7 @@
                     'type':     'image',
                     'upstream': upstreamReg,
                     'name':     'onosproject/onos',
-                    'digest':   'sha256:83aa5b1f43d4bf772929dc5aacf3f57cbd4467a4c7184586b53a35ea8a23226a'
+                    'digest':   'sha256:c7308d57bfefddb7a199ca7bd8ad77f837b31d3d853c13af0e98409e60cba229'
             ],
             'nginx': [
                     'type':     'image',