That's a trivial modification:

    $ echo linkedin | xargs node -e "var x = require('crypto').createHash('sha1').update(process.argv[1]).digest('hex'); console.log(x.substring(5));" | xargs -I {} grep {} hashes.txt

I'm surprised at the backlash to what I thought was fun code golfing. No one called me names after I posted a simple Python solution that didn't check the file. For what it's worth I've changed my LI password and I haven't bothered downloading the actual hash file.