Try to solve 'TaichiOperations' problem

[Magic-Xin]

I have a problem whit 'AttributeError: module 'taichi' has no attribute 'TaichiOperations'' error when I used taichi-tina in ver 0.1.1 and taichi in ver 0.7.16. I searched this from here, and it works well.

I'm a sophomore student from China, maybe my English and code is not so good, but I still hope this can help u.

[zhehaoli1999]

This pull request solves 'TaichiOperations' problem for me, thx!