Use LTS node on travis instead of node 10.0
Use LTS node on travis instead of node 10.0

It seems that node 10.0 may have issues installing JupyterLab.
bloomberg/bqplot,dmadeka/bqplot,ChakriCherukuri/bqplot,bloomberg/bqplot,ChakriCherukuri/bqplot,bloomberg/bqplot,dmadeka/bqplot,SylvainCorlay/bqplot,SylvainCorlay/bqplot,ssunkara1/bqplot,SylvainCorlay/bqplot,ssunkara1/bqplot,ChakriCherukuri/bqplot