doc: Fix typo (#1155)

Author: Komyyy

Batteries/Data/List/Basic.lean

@@ -515,7 +515,7 @@ def sigmaTR {σ : α → Type _} (l₁ : List α) (l₂ : ∀ a, List (σ a)) :
 def ofFnNthVal {n} (f : Fin n → α) (i : Nat) : Option α :=
   if h : i < n then some (f ⟨i, h⟩) else none
 
-/-- `disjoint l₁ l₂` means that `l₁` and `l₂` have no elements in common. -/
+/-- `Disjoint l₁ l₂` means that `l₁` and `l₂` have no elements in common. -/
 def Disjoint (l₁ l₂ : List α) : Prop :=
   ∀ ⦃a⦄, a ∈ l₁ → a ∈ l₂ → False