Removed 0.6 from travis, added 0.10

Also stringified the versions as they should be, as it is a yaml file so `0.10` becomes `0.1`, so for versions we should use strings - `"0.10"` stays `0.10`
Remove unnecessary comma from documentation

A comma is used when there are three or more items in a series or you are separating two or more independent clauses.
package: remove `optionalDependencies`
LICENSE: update
package: bump `engine.io`
updated history
Merge pull request #1220 from balupton/patch-1

Removed 0.6 from travis (no longer supported by socket.io deps), added 0.10
Merge pull request #1313 from tylermcginnis33/patch-1

Remove unnecessary comma from documentation