custom build without progress throws error

[zakness]

git clone git@github.com:petkaantonov/bluebird
git checkout v2.9.14
node tools/build --feature="core"

I loaded the resulting bluebird.js and got the following error:

Uncaught TypeError: undefined is not a function

Promise.prototype._migrateCallbacks = function (follower, index) {
    var fulfill = follower._fulfillmentHandlerAt(index);
    var reject = follower._rejectionHandlerAt(index);
    var progress = follower._progressHandlerAt(index);  // ← offending line (1796)
    var promise = follower._promiseAt(index);
    var receiver = follower._receiverAt(index);
    if (promise instanceof Promise) promise._setIsMigrated();
    this._addCallbacks(fulfill, reject, progress, promise, receiver);
};

node tools/build --feature="core progress" fixes the issue.