Build with Go 1.15, so it will work with latest macOS.

• Remove --parallel flag when pulling images, since this is the default as
  of Compose v1.21.0

support for labeling docker image with the project git repo url

• BREAKING elsy no longer swallows exit codes. This is a breaking change if you relied on exit codes always being 1.

• Fix issue where a docker-compose
  containing only services using local images would break bootstrapping. #88

• Add support for a local_images config in lc.yml. Images listed in this
  sequence will not be pulled during lc bootstrap. #84

Major version change because the exit code semantics around lc bootstrap have changed,
it now fails builds if images cannot be pulled.

• Improve lc bootstrap image pull logic so that elsy will never attempt to pull
  the image being packaged by the repo (i.e., the docker-image-name config). This
  means no more confusing error messages about "unable to pull image". #82
• Start failing builds if images could not be pulled, this is now possible because
  we are no longer attempting to pull the repo's image (see above bullet). #82
• Begin pulling images in parallel during lc bootstrap (requires compose 1.12.0 or higher).
  This can be disabled using the flag disable-parallel-pull. #80

• add resolve-docker-tag command

• lc teardown will now remove all networks created by the project ( #69 )

• Added lc system upgrade to fetch and install the latest verison of lc from Github.