Fix indentation for code block in changelog

This was showing up as an H1. Fixing the indentation here fixes the codeblock.

activerecord/CHANGELOG.md

@@ -4,10 +4,10 @@
 
     Example:
 
-    PriceEstimate.where(estimate_of: [Treasure.find(1), Car.find(2)])
-    # => SELECT "price_estimates".* FROM "price_estimates"
-         WHERE (("price_estimates"."estimate_of_type" = 'Treasure' AND "price_estimates"."estimate_of_id" = 1)
-         OR ("price_estimates"."estimate_of_type" = 'Car' AND "price_estimates"."estimate_of_id" = 2))
+        PriceEstimate.where(estimate_of: [Treasure.find(1), Car.find(2)])
+        => SELECT "price_estimates".* FROM "price_estimates"
+           WHERE (("price_estimates"."estimate_of_type" = 'Treasure' AND "price_estimates"."estimate_of_id" = 1)
+           OR ("price_estimates"."estimate_of_type" = 'Car' AND "price_estimates"."estimate_of_id" = 2))
 
     *Philippe Huibonhoa*