dockerfile: update to node 9
dockerfile: update to node 9

Use the latest version of nodejs.  This is to make sure we're
forwards-compatible.

Signed-off-by: Sean Cross <d7e19930cc1f42c2d0781f4d9e6f1fe5891bf9cf@xobs.io>

chibitronics/ltc-webview-layer,chibitronics/ltc-webview-layer,chibitronics/ltc-webview-layer,chibitronics/ltc-webview-layer