chore(tactic/field_simp): fix docstring (#13695)

src/tactic/field_simp.lean

@@ -43,7 +43,7 @@ If the goal is an equality, this simpset will also clear the denominators, so th
 can normally be concluded by an application of `ring` or `ring_exp`.
 
 `field_simp [hx, hy]` is a short form for
-`simp [-one_div, -mul_eq_zero, hx, hy] with field_simps {discharger := [field_simp.ne_zero]}`
+`simp [-one_div, -mul_eq_zero, hx, hy] with field_simps {discharger := tactic.field_simp.ne_zero}`
 
 Note that this naive algorithm will not try to detect common factors in denominators to reduce the
 complexity of the resulting expression. Instead, it relies on the ability of `ring` to handle