parsing fails on volumes using long syntax

[runar-indico]

If one is using the long volume-syntax, it will not be able to parse the file, like in the snippet below:

      - type: bind
        source: ./nginx.conf.default
        target: /etc/nginx/nginx.conf

Currently, the parser expects a string.

I added a PR in #167 to fix the issue.

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This project looks interesting.

[jdnordy]

PR #167 merged in! Soon to go live in v1.2.1