fix(server): switch to sync write

The async write operation has no callback and errors are not
detected that way. Switch to the sync version to circumvent that
problem.

lib/server.js

@@ -269,7 +269,7 @@ Server.prototype._start = function (config, launcher, preprocess, fileList,
         return logMap[m]
       })
       self.log.debug('Writing browser console line: %s', logString)
-      fs.write(browserLogFile, logString + '\n')
+      fs.writeSync(browserLogFile, logString + '\n')
     })
   }