Update required PyTorch version check

distiller/__init__.py

@@ -107,13 +107,13 @@ def model_find_module(model, module_to_find):
 
 def check_pytorch_version():
     from pkg_resources import parse_version
-    if parse_version(torch.__version__) < parse_version('1.1.0'):
+    required = '1.3.1'
+    actual = torch.__version__
+    if parse_version(actual) < parse_version(required):
         msg = "\n\nWRONG PYTORCH VERSION\n"\
-              "The Distiller \'master\' branch now requires at least PyTorch version 1.1.0 due to "\
-              "PyTorch API changes which are not backward-compatible. Version detected is {}.\n"\
-              "To make sure PyTorch and all other dependencies are installed with their correct versions, " \
-              "go to the Distiller repo root directory and run:\n\n"\
-              "pip install -e .\n".format(torch.__version__)
+              "Required:  {}\n" \
+              "Installed: {}\n"\
+              "Please run 'pip install -e .' from the Distiller repo root dir\n".format(required, actual)
         raise RuntimeError(msg)