rename dependency: to depends:

[dmalan]

For consistency with a standard key name, rather than use our own (more verbose) one.

[cmlsharp]

What makes "depends" standard? Why make this a verb when every other key is a noun?

EDIT: we also use dependencies as a key in the .cs50.yaml. Would you propose changing this as well?

[rongxin-liu]

Keeping dependency as the key name for now, since both depends and dependency would work. In case other people are already using the dependency key from our check50 JSON output, changing it to depends would be a breaking change, so it’s probably not worth it now.

cc @ivanharvard