Change flag for config file to "-c,--config"

[ohaiwalt]

Breaking change for anyone who may be specifying their relay config file from the command line.

$ ./relay --help
Usage of ./relay:
  -c, --config string       Path to configuration file
      --cpuprofile string   Write CPU profile to file
      --dev                 Enable developer mode
      --memprofile string   Write memory profile to this file

[sourcelevel-bot]

Ebert has finished reviewing this Pull Request and has found:

• 1 fixed issue! 🎉

You can see more details about this review at https://ebertapp.io/github/operable/go-relay/pulls/79.

[ohaiwalt]

Fixes #76

[coveralls]

Coverage remained the same at 20.893% when pulling ab7bec1 on ohaiwalt/config-flag into 858b8ff on master.

[agis]

I'm curious, what's the argument for breaking backwards compatibility by changing the flags?

P.S. This is more of a question to @vanstee who created the original issue (operable/cog#628).

[jesselang]

Can we keep compatibility and deprecate out --file with a warning instead of a breaking change?