redundant code in is_active_trail
Revert "update travis.yml"

This reverts commit cdafc22c6d88f0afb997344471fab3bfe3b84b39.
Revert "Revert "update travis.yml""

This reverts commit d0630250887fcadcf78b126a0c9a9288400ae04f.
Revert "redundant code in is_active_trail"

This reverts commit cee5ea538487b8ab0ea23567e6e8d558bbe5d718.
Merge branch 'dev' of https://github.com/pgmpy/pgmpy into dev
remove redundant code in is_active_trail function
replace add_nodes function with add_node and add_nodes_from
Merge pull request #33 from ankurankan/dev

replace add_nodes function with add_node and add_nodes_from