Error when bootstrapping minion in vagrant

gistfile1.txt

W: GPG error: http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4759FA960E27C0A6
 *  INFO: Running config_salt()
 *  INFO: Running install_ubuntu_stable()
Reading package lists...
Building dependency tree...
Reading state information...
The following extra packages will be installed:
  dctrl-tools debconf-utils libyaml-0-2 msgpack-python python-crypto
  python-jinja2 python-m2crypto python-markupsafe python-pkg-resources
  python-support python-yaml python-zmq salt-common
Suggested packages:
  debtags python-crypto-dbg python-crypto-doc python-jinja2-doc
  python-distribute python-distribute-doc
The following NEW packages will be installed:
  dctrl-tools debconf-utils libyaml-0-2 msgpack-python python-crypto
  python-jinja2 python-m2crypto python-markupsafe python-pkg-resources
  python-support python-yaml python-zmq salt-common salt-minion
0 upgraded, 14 newly installed, 0 to remove and 152 not upgraded.
Need to get 2,412 kB of archives.
After this operation, 9,467 kB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  python-zmq salt-common salt-minion
E: There are problems and -y was used without --force-yes
 * ERROR: Failed to run install_ubuntu_stable()!!!


Stderr from the command:

stdin: is not a tty