Fix bash variable errors at workflow builder cmd

[ghost]

Fixes #139

• Fix variable errors, use $
• Only scan for *.wf.yaml files as archive may contain other *.yaml files (happened in real use case)
• Fix parse call by removing wrong > redirection call

[erwinvaneyk]

Thanks @thenamly for your contribution 😁 I noticed issues 1 and 3 too in #135, but it is great to have that in earlier. The *.wf.yaml issue I had not thought of before--nice idea to narrow the selection. Although the original intention was not to require files to have the .wf.yaml extension; it is more of a convention. We might want to change that later to a more generalized approach, for example with a blacklist or whitelist file to indicate which files to parse.

Let me check if there is an easy way for me to trigger the builds on our repo, instead of yours, to fix the travis tests (they currently require a gcloud api key, which you of course don't have).

[erwinvaneyk]

I am going to defer the fixing of the CI for external contributions to a later time. The YAML constraint is good--at least for now (see other comment). So LGTM 👍