Fix pycodestyle issue E306

expected 1 blank line before a nested definition, found 0
sage/combinat/k_regular_sequence.py:1251:9: E306

Author: cheuberg

src/sage/combinat/k_regular_sequence.py

@@ -1248,6 +1248,7 @@ def find_linear_dependence(t_L, r_L, lines):
 
         to_branch = []
         lines = []
+
         def include(line):
             to_branch.append(line)
             lines.append(line)