Only use mercenary v0.3.5
Only use mercenary v0.3.5

v0.3.6 included a change that duplicated flags from parent commands,
resulting in, e.g, `usaidwat log --help` printing the options `-h`,
`-v`, and `-t` twice. I don't like that, but I don't expect mercenary to
change its behavior (since that was intentionally introduced in a recent
commit [1]), so I'll just make sure only v0.3.5 is being used.

    [1] https://github.com/jekyll/mercenary/pull/42

mdippery/usaidwat