Fix slackin

[shawwn]

Closes #379.

These changes are necessary in order for now rauchg/slackin to work.

The change to engine in package.json was derived from #379.

As for the change in hostname, I'm not sure why this is necessary. All I know is that when attempting to deploy using now, it passes in a bogus hostname. Hardcoding it to 0.0.0.0 fixes the issue (though it's admittedly a hack.)

[shawwn]

For posterity, the hostname error looks like this when attempting to deploy using now without hardcoding 0.0.0.0:

> [1] slackin@0.14.0 start /home/nowuser/src
> [1] chmod +x bin/slackin && ./bin/slackin
> [1] 
> [1] Tue Aug 21 2018 01:41:16 GMT+0000 (UTC) – fetching
> [1] events.js:160
> [1]       throw er; // Unhandled 'error' event
> [1]       ^
> [1] 
> [1] Error: getaddrinfo ENOTFOUND 1818o0VCBsQhSBxAwPQ9kXjS
> [1]     at errnoException (dns.js:28:10)
> [1]     at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:76:26)
> [1] 
> [1] npm ERR! Linux 4.14.19-coreos
> [1] npm ERR! argv "/usr/bin/node" "/usr/bin/npm" "start"
> [1] npm ERR! node v6.14.3
> [1] npm ERR! npm  v3.10.10
> [1] npm ERR! code ELIFECYCLE
> [1] npm ERR! slackin@0.14.0 start: `chmod +x bin/slackin && ./bin/slackin`
> [1] npm ERR! Exit status 1
> [1] npm ERR! 
> [1] npm ERR! Failed at the slackin@0.14.0 start script 'chmod +x bin/slackin && ./bin/slackin'.
> [1] npm ERR! Make sure you have the latest version of node.js and npm installed.
> [1] npm ERR! If you do, this is most likely a problem with the slackin package,
> [1] npm ERR! not with npm itself.
> [1] npm ERR! Tell the author that this fails on your system:
> [1] npm ERR!     chmod +x bin/slackin && ./bin/slackin
> [1] npm ERR! You can get information on how to open an issue for this project with:
> [1] npm ERR!     npm bugs slackin
> [1] npm ERR! Or if that isn't available, you can get their info via:
> [1] npm ERR!     npm owner ls slackin
> [1] npm ERR! There is likely additional logging output above.
> [1] 
> [1] npm ERR!     /home/nowuser/src/npm-debug.log
> [1] npm ERR! Please include the following file with any support request:
> [1] More details: https://err.sh/now-cli/no-open-port-found