fixed issue with fit method. Earlier was using ancestors method which used to return all the nodes above it in the family which we didn't need. Now have replaced it with predecessors
adds pandas to travis
Merge remote-tracking branch 'upstream/dev' into issue224

Conflicts:
	.travis.yml
	pgmpy/models/BayesianModel.py
Merge remote-tracking branch 'upstream/dev' into issue224
Merge pull request #238 from ankurankan/dev

skip test needs to fix
Merge remote-tracking branch 'upstream/dev' into issue224
Merge pull request #240 from ankurankan/dev

fixed factor product [fixes #233]
minor improvements in tests
minor improvements in tests [refs #241]
fixed factor_divide tests [fixes #241]
adds __truediv__ method to factors
adds test for truediv"
Merge pull request #242 from ankurankan/factor_divide

Factor divide
Merge remote-tracking branch 'upstream/dev' into issue224
Fixed typos in documentation and visual improvements.
Merge branch 'dev' of https://github.com/pgmpy/pgmpy into dev
Merge pull request #225 from ankurankan/issue224

Fit and predict methods for Bayesian Models
Modification in remove_cpds method for BayesianModel to take string as input.
Merge branch 'dev' of https://github.com/pgmpy/pgmpy into dev
Changed theme back to flatly.