Add missing command now required for code signing in travis. (#398)
Add missing command now required for code signing in travis. (#398)

See https://docs.travis-ci.com/user/common-build-problems/#mac-macos-sierra-1012-code-signing-errors
timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,OpenSmalltalk/vm,OpenSmalltalk/vm