Don't push non-release builds to bintray
Don't push non-release builds to bintray

We got a very nice email from JFrog letting us know we were using
bintray wrong and should be using Artifactory for nightlies. They
helpfully raised our limits temporarily until we get the situation
sorted.

This commit turns off sending non-releases to bintray. This can
be updated once we have an artifactory account to send non-releases
there.

dipinhora/ponyc,boemmels/ponyc,dipinhora/ponyc,boemmels/ponyc,kulibali/ponyc,boemmels/ponyc,Theodus/ponyc,sgebbie/ponyc,CausalityLtd/ponyc,Perelandric/ponyc,kulibali/ponyc,Perelandric/ponyc,jemc/ponyc,jupvfranco/ponyc,CausalityLtd/ponyc,kulibali/ponyc,Perelandric/ponyc,cquinn/ponyc,ponylang/ponyc,boemmels/ponyc,jupvfranco/ponyc,jupvfranco/ponyc,Theodus/ponyc,mkfifo/ponyc,Theodus/ponyc,boemmels/ponyc,mkfifo/ponyc,Perelandric/ponyc,jemc/ponyc,Theodus/ponyc,jupvfranco/ponyc,cquinn/ponyc,mkfifo/ponyc,Praetonus/ponyc,dipinhora/ponyc,cquinn/ponyc,Praetonus/ponyc,sgebbie/ponyc,mkfifo/ponyc,Praetonus/ponyc,ponylang/ponyc,ponylang/ponyc,Theodus/ponyc,sgebbie/ponyc,Praetonus/ponyc,mkfifo/ponyc,jupvfranco/ponyc,Perelandric/ponyc,sgebbie/ponyc,sgebbie/ponyc,CausalityLtd/ponyc,kulibali/ponyc,cquinn/ponyc,jemc/ponyc