Readme.md: Add Travis badge.
Readme.md: Add Travis badge.

jakirkham/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter,DudLab/rank_filter,nanshe-org/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter