only delete $app_path if $import_path is not empty
only delete $app_path if $import_path is not empty

This fixes https://github.com/gliderlabs/herokuish/issues/111
gliderlabs/herokuish,expa/herokuish,gliderlabs/herokuish,expa/herokuish,gliderlabs/herokuish,expa/herokuish,expa/herokuish,expa/herokuish,expa/herokuish,gliderlabs/herokuish,gliderlabs/herokuish,gliderlabs/herokuish,gliderlabs/herokuish,expa/herokuish,gliderlabs/herokuish,expa/herokuish