fixes error in XMLBIF writer class
fixes error in XMLBIF writer class

pgmpy/pgmpy,kris-singh/pgmpy,yashu-seth/pgmpy,abinashpanda/pgmpy,jhonatanoliveira/pgmpy,abinashpanda/pgmpy,pratyakshs/pgmpy,anaviltripathi/pgmpy,ankurankan/pgmpy,liquidmetal/pgmpy,yashu-seth/pgmpy,khalibartan/pgmpy,palashahuja/pgmpy,anaviltripathi/pgmpy,sandeepkrjha/pgmpy,palashahuja/pgmpy,pgmpy/pgmpy,khalibartan/pgmpy,ankurankan/pgmpy,sandeepkrjha/pgmpy,jhonatanoliveira/pgmpy,liquidmetal/pgmpy,pratyakshs/pgmpy,kris-singh/pgmpy