Add sudo apt-get update to circle.yml

circle.yml

@@ -26,6 +26,7 @@ dependencies:
         docker save weaveworks/weave-build >$WEAVE_BUILD;
       fi
   post:
+    - sudo apt-get update
     - sudo apt-get install bc jq
     - pip install requests
     - curl https://sdk.cloud.google.com | bash