Adjust imputation conditional statement

[ChadFibke]

Description

Addresses bug noted in #35 , which allows estimation of causal effects from both rb, and gformula models using estimation = "imputation" from cmest() and cmsens().

Changes

The following minor fix has been added to est.rb() and est.gformula()

if (is_glm_yreg && family_yreg$family %in% c("binomial", "quasibinomial") &&
          family_yreg$link == "logit")