fix travis builds

[graingert]

No description provided.

[doowb]

Thanks for the PR, but the real issue is that the version of mocha is wrong. Will you update this to just change the version of mocha to 3.5.3, change the engine back to 0.10.0 and add node 0.10 and 0.12 back to the build matrix?

Newer versions of mocha use dependencies that require higher versions of node, so we can't use those to test code that's compatible with older versions of node.

Thanks!

[jonschlinkert]

add node 0.10 and 0.12 back to the build matrix?

Not build matrix, just the node_js property.