Fix spurious error message in build/checkversion.py
Fix spurious error message in build/checkversion.py

There is a meaningless and unhelpful error message appearing at publish
time with some npm versions.  Suppress it by including stderr into the
captured stdout.

Change-Id: I73693433e5df5cc8d63375c08f765fbbb801f10f

vimond/shaka-player,russitto/shaka-player,TobbeEdgeware/shaka-player,indiereign/shaka-player,Ross-cz/shaka-player,indiereign/shaka-player,indiereign/shaka-player,Ross-cz/shaka-player,russitto/shaka-player,brightcove/shaka-player,vimond/shaka-player,TobbeEdgeware/shaka-player,russitto/shaka-player,tvoli/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,Ross-cz/shaka-player,vimond/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,TheModMaker/shaka-player,TobbeEdgeware/shaka-player,shaka-project/shaka-player,brightcove/shaka-player,shaka-project/shaka-player,TheModMaker/shaka-player,brightcove/shaka-player,TheModMaker/shaka-player