shortId are not as random as it does

[lchenay]

Here a test script:

genId = require "mongoose-shortid/lib/genid"
async = require "async"

async.times 50, (n, next) ->
    genId {base: 32, len: 6}, next
, (err, ids) ->
    console.log(ids)

Result: ADGPGP, ABIVDY, AG7DXM, AJUM5Q, AL7ZBR, AHQGXP, AFB64P, AP4GKA, ADSX37, AHXJ2I, AN3XR5, AACFOX, AAYVH5, ANUNBK, AO4PG6, ALVZIQ, AHXHM6, AGX2PO, AGRN4C, AJM4FZ, AJQWMS, ANWHML, AOVNTM, ACHBAX, AOD7A4, AEI5K2, AGRSAR, ALLBMG, AHIN3X, AFAGIZ, ALAIXW, AHOLXE, AMFCE7, ACSBRG, AIR6FA, AG7AZC, AMK3VP, AAEQSV, AK7Z6K, AOXEUY, AMONNC, ALUQP2, AMJNE2, ADQPMS, ACKNIX, ACI3MF, AIE3BC, ABHKXC, AC5LDX, AMWWTV