Android : google app engine java endpoints for android backend ./gradlew: No such file or directory error

I worked out example using this reference site: https://github.com/GoogleCloudPlatform/gradle-appengine-templates/tree/master/HelloEndpoints

when i worked all this step by step execute ./gradlew backend:appengineUpdate command when i excecute that line below error come:

./gradlew backend:appengineUpdate
bash: ./gradlew: No such file or directory

please tell me how to solve this error