MAINT: add pandas to requirements (for TravisCI)
MAINT: add pandas to requirements (for TravisCI)

altair-viz/altair,tacaswell/altair,alope107/altair,wrobstory/altair,jakevdp/altair,alope107/altair,freeman-lab/altair,wrobstory/altair,tacaswell/altair,freeman-lab/altair,kootenpv/altair,ellisonbg/altair,kootenpv/altair