Explicitly mention Python 2.7
Explicitly mention Python 2.7

to save people's time reproducing the experiment using Python 3

cshallue/models,tombstone/models,tombstone/models,alexgorban/models,cshallue/models,derekjchow/models,tombstone/models,cshallue/models,tombstone/models,derekjchow/models,cshallue/models,derekjchow/models,cshallue/models,tombstone/models,alexgorban/models,derekjchow/models,alexgorban/models,alexgorban/models,tombstone/models,alexgorban/models,derekjchow/models