Use -z instead of exclaimation point

Author: Josh Deffibaugh

.travis.yml

@@ -23,4 +23,4 @@ before_script:
   - adb shell input keyevent 82 &
 script:
   - ./gradlew testAllModules
-  - if [ [ [ "$TRAVIS_BRANCH" == "beta" ] || [ "$TRAVIS_BRANCH" == "master" ] ] && [! "$TRAVIS_TAG"] ]; then ./gradlew ship; fi
+  - if [ [ [ "$TRAVIS_BRANCH" == "beta" ] || [ "$TRAVIS_BRANCH" == "master" ] ] && [ -z "$TRAVIS_TAG"] ]; then ./gradlew ship; fi