[bug] --help doesn't print entire output

[vsoch]

With the latest release, container-diff --help doesn't print anything as it should (see #301 (comment))

Expected behavior

container-diff --help
container-diff is a CLI tool for analyzing and comparing container images.

Images can be specified from either a local Docker daemon, or from a remote registry.
To specify a local image, prefix the image ID with 'daemon://', e.g. 'daemon://gcr.io/foo/bar'.
To specify a remote image, prefix the image ID with 'remote://', e.g. 'remote://gcr.io/foo/bar'.
If no prefix is specified, the local daemon will be checked first.

Tarballs can also be specified by simply providing the path to the .tar, .tar.gz, or .tgz file.

Usage:
  container-diff [command]

Available Commands:
  analyze     Analyzes an image: [image]
  diff        Compare two images: [image1] [image2]
  help        Help about any command
  version     Print the version of container-diff

Flags:
      --format string      Format to output diff in.
  -h, --help               help for container-diff
  -v, --verbosity string   This flag controls the verbosity of container-diff. (default "warning")

Use "container-diff [command] --help" for more information about a command.

Actual behavior

$ container-diff --help
Usage of container-diff:

Information

• OS: Tested on ubuntu 18.04, 16.04, and archlinx (see issue linked above)
• container-diff version: v0.15.0

Steps to reproduce the behavior

Install container-diff as specific for linux in the README.md, and then run container-diff --help.

[Dhron]

@vsoch hey, could I try fixing this one? =)

[vsoch]

of course! @donmccasland is master and commander, but you also have my dinosaur blessing ✨

[vsoch]

Note that the cobra issue linked above is being marked as stale, so likely help won't come from there, unless someone wants to comment / unmark as stale here that is interested in working on this.

[lplazas]

@vsoch If still unassigned I'd love to give this one a try.

[vsoch]

@lplazas I'd say go for it - it's been a long time since October 19th, and if you have bandwidth, it's a +1 from me!

[nkubala]

@lplazas yeah go for it! and @vsoch good to see you still hanging out around here :)

[vsoch]

Always! I love containers, although I haven't done work with container-diff recently. People aren't as interested in metadata / provenance -type stuffs as I wish they would be :)

[nkubala]

yeah they like to leave the dirty work to us :)

not sure if you're working on Kubernetes stuff, but if you are be sure to check out skaffold!

[lplazas]

Alright, I'll work on it.

[lplazas]

@nkubala @vsoch please take a look at the PR when you have some time.