only deploy on heroku when php 5.6 build is successful
only deploy on heroku when php 5.6 build is successful

before travis tried to deploy on successful php 5.6 and php 7.0 builds
which lead to errors (e.g. database was dropped)

projektmotor/surveythor-demo,projektmotor/surveythor-demo,projektmotor/surveythor-demo,projektmotor/surveythor-demo