Fix torchvision pretrained deprecation warning

Author: jojje

Diff for: simclr/modules/resnet.py

@@ -3,8 +3,8 @@
 
 def get_resnet(name, pretrained=False):
     resnets = {
-        "resnet18": torchvision.models.resnet18(pretrained=pretrained),
-        "resnet50": torchvision.models.resnet50(pretrained=pretrained),
+        "resnet18": torchvision.models.resnet18(weights=torchvision.models.ResNet18_Weights.DEFAULT),
+        "resnet50": torchvision.models.resnet50(weights=torchvision.models.ResNet50_Weights.DEFAULT),
     }
     if name not in resnets.keys():
         raise KeyError(f"{name} is not a valid ResNet version")