message: detect weixin application environment
diff: var env = {};
  if (typeof navigator === 'undefined') {
  + if (wx && wx.version) {
  + // In Weixin Application
  + env = {
  + browser: {},
  + os: {},
  + node: false,
  + wxa: true, // Weixin Application
  + canvasSupported: true,
  + svgSupported: false
  + }
  + }
  + else {
  // In node
  env = {
  browser: {},
  os: {},
  node: true,
  + wxa: false,
  // Assume canvas is supported
  canvasSupported: true,
  svgSupported: true
  };
  }
  +}
  else {
  env = detect(navigator.userAgent);
  }
  