Apply Layout/SpaceInLambdaLiteral rubocop rule

I had mixed feelings about this rule, since I like spaces where
possible.

However, I changed my mind when I realized writing `->(thing) { }` was
similar to defining a method, and we don't have a space before the
parenthesis when defining a method.

app/models/user.rb

@@ -123,7 +123,7 @@ class User < ApplicationRecord
     string = "%#{search_string}%"
     where("username ILIKE ? OR email ILIKE ? OR document_number ILIKE ?", string, string, string)
   end
-  scope :between_ages, -> (from, to) do
+  scope :between_ages, ->(from, to) do
     where(
       "date_of_birth > ? AND date_of_birth < ?",
       to.years.ago.beginning_of_year,