For some reason the command npm outdated --json --long which is used in [1] returns 0 in version 6 and 1 for version 7. To reproduce:

nvm use v6.9.4
npm outdated  --json --long
echo $?
nvm use v7.4.0
npm outdated  --json --long
echo $?

because of the difference in return code [2] triggers an error. The output is the same though so it should just continue running.

[1] https://github.com/facebook/fbjs/blob/master/packages/fbjs-scripts/gulp/check-dependencies.js#L26
[2] https://github.com/facebook/fbjs/blob/master/packages/fbjs-scripts/gulp/check-dependencies.js#L38