Fix expected timestamp value restJson1 defaults test

This commit updates the expected `defaultTimestamp` in a restJson1
defaults test to 2. The value 1 may have been incorrectly copied
from the corresponding test in Rails Json where the timestamp format
is httpdate instead of epoch seconds.

smithy-aws-protocol-tests/model/restJson1/defaults.smithy

@@ -323,7 +323,7 @@ apply OperationWithDefaults @httpResponseTests([
  defaultDocumentBoolean: false
  defaultDocumentList: ["b"]
  defaultNullDocument: "notNull"
- defaultTimestamp: 1
+ defaultTimestamp: 2
  defaultBlob: "hi"
  defaultByte: 2
  defaultShort: 2
@@ -457,4 +457,4 @@ enum TestEnum {
 intEnum TestIntEnum {
  ONE = 1
  TWO = 2
-}
+}