Edit trait

Related to <a href="https://ebi-forecast.igb.illinois.edu/redmine/issues/2198">#2198</a> and <a href = "https://ebi-forecast.igb.illinois.edu/redmine/issues/2351">#2351</a>
If you use @trait.errors.add(:covariates, ...) instead of the << operator, this
will make a new "covariates" key if it doesn't exist, and it will add to the array value belonging to the "covariates" key
if it _does_ exist.  This will allow you to reduce the preceding 4 lines down to one.  See http://apidock.com/rails/v4.0.2/ActiveModel/Errors/add for more information.