docs: typo fix (#62)

@m0un10 Thanks for this fix!

docs/resources/stripe_coupon.md

@@ -28,9 +28,9 @@ resource "stripe_coupon" "coupon" {
 
 // coupon for the percentage off discount
 resource "stripe_coupon" "coupon" {
-  name            = "33.3% discount"
-  percentage_off  = 33.3
-  duration        = "forever"
+  name        = "33.3% discount"
+  percent_off = 33.3
+  duration    = "forever"
 }
 
 // coupon with limitation to a date and the product only
@@ -75,4 +75,4 @@ Attributes exported by this resource include:
 * `times_redeemed` - Int. Number of times this coupon has been applied to a customer.
 * `applies_to` - List(String). A list of product IDs this coupon applies to.
 * `valid` - Bool. Taking account of the above properties, whether this coupon can still be applied to a customer.
-* `metadata` - Map(String). Set of key-value pairs attached to an object.
+* `metadata` - Map(String). Set of key-value pairs attached to an object.