Add --no-check-certificate to wget when retrieving omnibus installer

On one of my debian box, I kept on getting the following error and can't go further when I do knife solo prepare:

--2013-05-07 01:01:05--  https://www.opscode.com/chef/install.sh
Resolving www.opscode.com... 184.106.28.82
Connecting to www.opscode.com|184.106.28.82|:443... connected.
ERROR: cannot verify www.opscode.com’s certificate, issued by “/C=US/O=DigiCert Inc/CN=DigiCert Secure Server CA”:
  Unable to locally verify the issuer’s authority.
To connect to www.opscode.com insecurely, use ‘--no-check-certificate’.