Should check packet.id for non-null, not 0

Like the server does!!!
Merge pull request #609 from kevin-roark/fix/event-emitter-callback-bug

Should check packet.id for non-null, not 0
Remove require fs in lib/index.js
Update .travis.yml

Remove 0.8 from travis.yml in socket.io-client
fixed zuul redirect bug

url() has optional parameter loc
updated zuul to latest version
Merge pull request #615 from bmalehorn/zuul_update

updated zuul to latest version
Merge pull request #614 from bmalehorn/zuul_fix

fixed zuul redirect bug
Merge pull request #613 from grant/patch-1

Update .travis.yml
Merge pull request #611 from poohlty/remove-require-fs

Remove require fs in lib/index.js