Default value for 'c' doesn't proprogate to argv.concurrency

Output

$ ./test.js -b my-bucket
Bucket=my-bucket
Concurrency=3
Bucket=my-bucket
Concurrency=undefined

test.js

#!/usr/bin/env node

var argv = require('optimist')
    .usage('Usage: $0 --bucket name')

    .demand('b')
    .alias('b', 'bucket')
    .describe('b', 'bucket to sync with')

    .describe('c', 'concurrency level for uploads/downloads')
    .alias('c', 'concurrency')
    .default('c', 3)

    .argv;


console.log('Bucket=' + argv.b);
console.log('Concurrency=' + argv.c);

console.log('Bucket=' + argv.bucket);
console.log('Concurrency=' + argv.concurrency);