Don't call npm update when building installer.

Calling "npm update" plops a newer version of request into the
adal-node node_modules directory which has a bug in it.
By not calling npm update, we use the old (old, old) version of
request that xplat uses which does not have bugs that we hit.
Merge pull request #1362 from christav/osx-installer-fix

Don't call npm update when building installer.