Can't install phantomjs in shinyapps.io

When I publish a Rselenium shiny app, I got this error:

E: Package 'phantomjs' has no installation candidate## End Task Log ################################################################
Error: Unhandled Exception: Child Task 1355100025 failed: Error building image: Build exited with non-zero status: 100
Execution halted

How can I fix this problem?