updated to refresh 'apt-get' source list

Author: ivailop

shippable.yml

@@ -7,6 +7,7 @@ env:
 
 build:
  ci:
+  - sudo apt-get update
   - sudo apt-get install cmake
   - sudo pip install gcovr
   - wget https://github.com/google/googletest/archive/release-1.8.0.zip