Fix incorrect usage of change_column

Addressing:
-- change_column(:scaptimony_scap_contents, :title, {:null=>false})
rake aborted!
An error has occurred, this and all later migrations canceled:

undefined method `to_sym' for {:null=>false}:Hash
Introduce ScapContentProfile class to SCAPtimony model

An object of category (#ScapContentProfile) is any xccdf:Profile referenced
from ScapContent (XML file that can fed to SCAP scanner).
Parse xccdf:Profiles to the ScapContentProfile table.