Baleen's container naming is not compatible with Fig

[holic]

I am using a repo with a hyphen in the name. Initially, I had named the container to match (via baleen.yml), but we found that this would cause troubles in Fig. So I renamed the container name, but the dir name is used as a surrogate for the project name when issuing a --build, so it's still mucking with Fig's naming.

Until this is fixed, it might be worth using some sort of slugify method to strip any characters that do not match [0-9a-z_].