Ignoring yarn in slug

[albatrocity]

Fixes #142, phantomjs-prebuilt issues (see this)

[albatrocity]

@dmdez @roblafeve confirmed, this fixes #142. How do we feel about abandoning yarn, at least on Heroku?

[dmdez]

Only other idea I had was to find a way to keep yarn and disable on heroku deployments (somehow).

[dmdez]

Looks like we should be able to add yarn.lock to a .slugignore file? Much like a .gitignore.
https://devcenter.heroku.com/articles/slug-compiler#ignoring-files-with-

If this works, we can keep yarn for our own selfish needs.... However, one could still run into yarn build issues locally.

[albatrocity]

@dmdez it's auto-detected, but maybe we could do a postinstall hook that runs npm install pantomjs-prebuilt?

[albatrocity]

Ah, nice, I'll try a .slugignore

[albatrocity]

@dmdez bingo, that works. Local stuff can still be run with yarn dev, etc.

[roblafeve]

Crisis averted 😄

[dmdez]

Merge away as you wish

[albatrocity]

@dmdez you should have what you need for #95 in master now 😁 (only for new completions for now)