Typo in log_variational_posterior computation

[shishir13sharma]

The return statement should be:
return self.l1.log_variational_posterior
+ self.l2.log_variational_posterior
+ self.l3.log_variational_posterior
instead of the current :
return self.l1.log_variational_posterior
+ self.l2.log_variational_posterior
+ self.l2.log_variational_posterior
Currently, the log posterior of l2 is being counted twice and the log posterior of l3 is not being taken into account at all.