Handle non_hex_deps exception

[tsloughter]

Trying to publish a package of an app with a non-hex dep rightly fails but the error isn't properly handled so you'll get the message to rerun with DIAGNOSTIC=1 and then something like:

===> Unknown error: {create_package,
                        {error,{non_hex_deps,["eqwalizer_support"]}}}

[starbelly]

huh, where was this being published to?

[tsloughter]

Standard hexpm.

[starbelly]

How do you propose we handle this? Presumably, you mean that if you're publishing to hex and a dep is say a git repo, or some other non-hex dep, but the app that is being published can be published anyway without the lock to said non-hexpm?