Fix erroneous tuple parsing

trans/transpiler/phases/typing/stdlib.py

@@ -60,7 +60,7 @@ class StdlibVisitor(NodeVisitorSeq):
                 if isinstance(b.slice, ast.Name):
                     sliceval = [b.slice.id]
                 elif isinstance(b.slice, ast.Tuple):
-                    sliceval = [n.id for n in b.slice.value.elts]
+                    sliceval = [n.id for n in b.slice.elts]
                 if isinstance(b.value, ast.Name) and b.value.id == "Generic":
                     typevars = sliceval
                 elif isinstance(b.value, ast.Name) and b.value.id == "Protocol":