Specify supported Python versions in classifiers
Specify supported Python versions in classifiers

Namely this supports 2.7 and 3.4-3.6.

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