Fix deprecation warning (#13)

Replace `triangular_solve()` with `linalg.solve_triangular()` to
fix the deprecation warning. See also:

#12

normflows/flows/mixing.py

@@ -434,11 +434,11 @@ def inverse_no_cache(self, inputs):
         """
         lower, upper = self._create_lower_upper()
         outputs = inputs - self.bias
-        outputs, _ = torch.triangular_solve(
-            outputs.t(), lower, upper=False, unitriangular=True
+        outputs = torch.linalg.solve_triangular(
+            lower, outputs.t(), upper=False, unitriangular=True
         )
-        outputs, _ = torch.triangular_solve(
-            outputs, upper, upper=True, unitriangular=False
+        outputs = torch.linalg.solve_triangular(
+            upper, outputs, upper=True, unitriangular=False
         )
         outputs = outputs.t()