Added coverage to tests

.travis.yml

@@ -37,3 +37,4 @@ script:
 - pwd
 - ./tool/travis.sh notus
 - ./tool/travis.sh zefyr
+- bash <(curl -s https://codecov.io/bash)

packages/zefyr/tool/travis.sh

@@ -2,4 +2,4 @@
 
 set -e
 
-$TRAVIS_BUILD_DIR/flutter/bin/flutter test
+$TRAVIS_BUILD_DIR/flutter/bin/flutter test --coverage