Update README.md

Modified the onAll example to have the correct arity. For unknown reasons in the example the onAll method was being passed the orchestrator instance in addition to the callback.
Merge pull request #43 from chrisakers/patch-1

Update README.md
drop unsupported travis versions

travis only supports the last stable, the current stable, and the current unstable.
Merge branch 'master' into blaine

Conflicts:
	.travis.yml