Previously the `mix deps.patch` task lived at `lib/mix/tasks/deps.patch.ex`
and the `deps.get` alias invoked it. This broke `mix deps.get --only prod`
in Docker: `lib/` isn't compiled yet when deps are fetched, so the task
module couldn't be resolved and the build failed with
`The task "deps.patch" could not be found`.
Move the patch-application function directly into `mix.exs` as a private
helper and wire it into the alias via `&apply_dep_patches/1`. `mix.exs` is
always loadable, so the function is available the moment `deps.get` runs.
Graham McIntire
6c6e413105