Can't call the assemble script when providing the scripts url using -s option

I am trying to use the sti and provide a url to the sti scripts as follows:

sti build https://github.com/iocanel/test-sti.git fabric8/karaf-2.4 fabric8/test-sti -s file:/somepath/.sti/bin

The error I am getting is:

/bin/bash: assemble: No such file or directory
An error occured: Container exited with exit code: 127
