Added coverage to tests

.travis.yml

 - pwd
 - ./tool/travis.sh notus
 - ./tool/travis.sh zefyr
+- bash <(curl -s https://codecov.io/bash)

packages/zefyr/tool/travis.sh

 
 set -e
 
-$TRAVIS_BUILD_DIR/flutter/bin/flutter test
+$TRAVIS_BUILD_DIR/flutter/bin/flutter test --coverage