Dockerfile: build a new 'fly' inline
Dockerfile: build a new 'fly' inline

this way PR builds and such will run with the latest fly changes, rather
than running with the fly that was built in concourse/dev from master

Signed-off-by: Alex Suraci <925ba519bbf1a06224928b692ef88b93aee946af@gmail.com>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse