Fix revdep_script
Fix revdep_script

When execution gets here, we are hit by NoMethodError.
See, for example, https://travis-ci.org/davidgohel/rvg/jobs/172562948.

JuliaCI/travis-build,craigcitro/travis-build,andyli/travis-build,andyli/travis-build,JuliaCI/travis-build,craigcitro/travis-build,kevmoo/travis-build,kevmoo/travis-build