"npm link" vanadium instead of "npm install"
"npm link" vanadium instead of "npm install"

"npm install" puts a full copy of vanadium inside the travel repo,
including the .jiri metadata file.

This confuses jiri tool because it finds two projects with the same name
at different paths in the project tree.

"npm link" creates symlinks, which jiri will not follow, thus avoiding
this issue.

All of our projects currently use "npm link", except for travel.  At
some point we will want to do something better than "npm link", but this
is good enough for now.

Change-Id: Iad79f57a81b64908176e94d6487877b8cfbb5bc0

vanadium/travel,vanadium/travel,vanadium/travel