Exclude node_js 6 on windows on travis.
Exclude node_js 6 on windows on travis.

Cycling74/node-midi,Cycling74/node-midi,Cycling74/node-midi,Cycling74/node-midi,justinlatimer/node-midi,Cycling74/node-midi,Cycling74/node-midi,justinlatimer/node-midi,justinlatimer/node-midi