[minor] reformat setup.py

Author: Zhijian Liu

setup.py

@@ -3,7 +3,7 @@
 from setuptools import find_packages, setup
 
 from torch.utils.cpp_extension import BuildExtension, CppExtension, CUDAExtension, CUDA_HOME
-has_cuda = (torch.cuda.is_available() and CUDA_HOME is not None) or os.getenv("FORCE_CUDA", "0") == "1"
+has_cuda = (torch.cuda.is_available() and CUDA_HOME is not None) or os.getenv('FORCE_CUDA', '0') == '1'
 
 from torchsparse import __version__