add --skip-install flag
add --skip-install flag

I often code on the bus or places without internet.  Because of the missing packages check, I can't run my tests in these situations.

This change makes it possible to opt out of the package check so I can run my tests again without wifi.
rtfeldman/node-elm-test,rtfeldman/node-test-runner,ento/node-elm-test,ento/node-elm-test,rtfeldman/node-elm-test