run step seems to be running asynchronously instead of synchronously

[kensoh]

The following script, when run on macOS, completes in 8 seconds instead of 1 + 4 + 8 = 13 seconds. It appears that run step execute asynchronously. An issue raised to CasperJS repo for review and discussion, but going to implement an interim solution into TagUI in the meantime.

run sleep 1
echo '1'

run sleep 4
echo '2'

run sleep 8
echo '3'

[kensoh]

With above commit, the cutting edge version will run the example above finishing in 13 seconds.

[kensoh]

(changing to query as it is an upstream query to CasperJS)