Update ws to next major version (when it's released)

[feross]

Because of issues like this one: mafintosh/torrent-stream#137 (comment)

[feross]

Another reason to get rid of this dep is that on an OS X machine with the command line tools installed, but no Xcode, this error is spewed upon installing WebTorrent:

npm WARN engine windows-no-runnable@0.0.6: wanted: {"node":"0.6"} (current: {"node":"0.12.7","npm":"2.11.3"})

> bufferutil@1.1.0 install /usr/local/lib/node_modules/webtorrent/node_modules/torrent-discovery/node_modules/bittorrent-tracker/node_modules/ws/node_modules/bufferutil
> node-gyp rebuild

xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

  CXX(target) Release/obj.target/bufferutil/src/bufferutil.o
  SOLINK_MODULE(target) Release/bufferutil.node

> utf-8-validate@1.1.0 install /usr/local/lib/node_modules/webtorrent/node_modules/torrent-discovery/node_modules/bittorrent-tracker/node_modules/ws/node_modules/utf-8-validate
> node-gyp rebuild

xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

  CXX(target) Release/obj.target/validation/src/validation.o
  SOLINK_MODULE(target) Release/validation.node

[No9]

+1 for removing as many native deps as possible

[mafintosh]

We could PR the two native deps to switch to prebuild and then add have them fallback to the js libraries if no prebuild is available

[feross]

websockets/ws#577

[feross]

The ws package just removed its native dependencies, so as soon as they publish that to npm, we can bump the version here and this will no longer be an issue!

websockets/ws@49b1109

[feross]

This is done, released as 7.0.0.