Move en-US.yml's cell_phone entry to the correct position (#2924)

`PhoneNumber.cell_phone` expects an i18n key of `cell_phone.formats`,
but the en-US.yml file currently has `faker.phone_number.cell_phone`
instead of `faker.cell_phone`.

The result of that mismatch is that `cell_phone` will ignore the defined
formats, and potentially generate invalid US numbers (e.g. those with an
area code beginning with 1) when the locale is en-US.

31d99d1 reworked YAML structure and
appears to have inadvertently moved the key.

You can see the change in US number behavior in a console:

  Faker::Config.locale = "en-US"
  Faker::PhoneNumber.translate("faker.cell_phone.formats")

On 3.3.0 this returns

  ["###-###-####", "(###) ###-####", "###.###.####", "### ### ####"]

because it's the fallback value within the `en` (not `en-US`) locale
file. The correct value should be the formats outdented in this commit.

lib/locales/en-US.yml

@@ -6949,16 +6949,16 @@ en-US:
         - "(#{PhoneNumber.area_code}) #{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number} x#{PhoneNumber.extension}"
         - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number} x#{PhoneNumber.extension}"
         - "#{PhoneNumber.area_code}.#{PhoneNumber.exchange_code}.#{PhoneNumber.subscriber_number} x#{PhoneNumber.extension}"
-      cell_phone:
-        formats:
-          - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
-          - "(#{PhoneNumber.area_code}) #{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
-          - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
-          - "#{PhoneNumber.area_code}.#{PhoneNumber.exchange_code}.#{PhoneNumber.subscriber_number}"
-          - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
-          - "(#{PhoneNumber.area_code}) #{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
-          - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
-          - "#{PhoneNumber.area_code}.#{PhoneNumber.exchange_code}.#{PhoneNumber.subscriber_number}"
+    cell_phone:
+      formats:
+        - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
+        - "(#{PhoneNumber.area_code}) #{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
+        - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
+        - "#{PhoneNumber.area_code}.#{PhoneNumber.exchange_code}.#{PhoneNumber.subscriber_number}"
+        - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
+        - "(#{PhoneNumber.area_code}) #{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
+        - "#{PhoneNumber.area_code}-#{PhoneNumber.exchange_code}-#{PhoneNumber.subscriber_number}"
+        - "#{PhoneNumber.area_code}.#{PhoneNumber.exchange_code}.#{PhoneNumber.subscriber_number}"
     id_number:
       valid: "#{IdNumber.ssn_valid}"
       invalid: