'async' is a reserved word in Python >= 3.7

Change these instances of 'async' to '__non_blocking__' in sync with pytorch/pytorch#4999

flake8 testing of https://github.com/SeuTao/RSNA2019_1st_place_solution on Python 3.8.0

$ flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics

./2DCNN/src/predict.py:285:55: E999 SyntaxError: invalid syntax
        labels = labels.view(-1, 6).contiguous().cuda(async=True)
                                                      ^
./2DCNN/src/train.py:54:55: E999 SyntaxError: invalid syntax
        target = target.view(-1, 6).contiguous().cuda(async=True)
                                                      ^
./2DCNN/src/tuils/swa_utils.py:63:30: E999 SyntaxError: invalid syntax
        inputs = inputs.cuda(async=True)
                             ^
3     E999 SyntaxError: invalid syntax
3

https://flake8.pycqa.org/en/latest/user/error-codes.html

On the flake8 test selection, this PR does not focus on "style violations" (the majority of flake8 error codes that psf/black can autocorrect). Instead these tests are focus on runtime safety and correctness:

E9 tests are about Python syntax errors usually raised because flake8 can not build an Abstract Syntax Tree (AST). Often these issues are a sign of unused code or code that has not been ported to Python 3. These would be compile-time errors in a compiled language but in a dynamic language like Python they result in the script halting/crashing on the user.
F63 tests are usually about the confusion between identity and equality in Python. Use ==/!= to compare str, bytes, and int literals is the classic case. These are areas where a == b is True but a is b is False (or vice versa). Python >= 3.8 will raise SyntaxWarnings on these instances.
F7 tests logic errors and syntax errors in type hints
F82 tests are almost always undefined names which are usually a sign of a typo, missing imports, or code that has not been ported to Python 3. These also would be compile-time errors in a compiled language but in Python a NameError is raised which will halt/crash the script on the user.

SeuTao / RSNA2019_Intracranial-Hemorrhage-Detection

'async' is a reserved word in Python >= 3.7 #2