Fix type annotation of GlobalAvgPool and GlobalMaxPool (#154)

Author: Zhijian Liu

torchsparse/nn/modules/pooling.py

@@ -1,3 +1,4 @@
+import torch
 from torch import nn
 
 from torchsparse import SparseTensor
@@ -8,11 +9,11 @@
 
 class GlobalAvgPool(nn.Module):
 
-    def forward(self, input: SparseTensor) -> SparseTensor:
+    def forward(self, input: SparseTensor) -> torch.Tensor:
         return F.global_avg_pool(input)
 
 
 class GlobalMaxPool(nn.Module):
 
-    def forward(self, input: SparseTensor) -> SparseTensor:
+    def forward(self, input: SparseTensor) -> torch.Tensor:
         return F.global_max_pool(input)