Restore browser tests

[vweevers]

Over at Airtap (airtap/airtap#171) we have been wondering which browsers readable-stream will target, if and when browser tests are restored. Specifically whether IE9 and IE10 support is still required?

I can do a PR to setup airtap, unless you want to wait for a stable release (airtap/airtap#170).

@mcollina /cc @feross @ralphtheninja

[mcollina]

I have been working on readable-stream@3 at https://github.com/nodejs/readable-stream/commits/next. I do not have all tests passing yet.

It would be fantastic to have airtap supported there, and I think won't need IE9 and IE10 support there anyway.

Would you like to send a PR against that? The 2.x line should support IE9 and IE10, even thought we are not really testing them at this point.

[vweevers]

Would you like to send a PR against that?

Sure! I noticed you removed the matrix from .travis.yml (e9cde33). Do you want me to wait until the tests are passing in node?

[mcollina]

@vweevers feel free to re-add the matrix for the browser things. We will not be supporting ancient Node anymore.

[vweevers]

Opera 11 (fd1efbf) is also pretty old, and the version range 11..latest is huge. Perhaps the target should be -3..latest like the other evergreen browsers?

[vweevers]

It would be fantastic to have airtap supported there, and I think won't need IE9 and IE10 support there anyway.

cc @jhiesey because you said you want IE9/10 in stream-http which depends on readable-stream.

[mcollina]

@vweevers +1 of having the same range.

[vweevers]

#340