Accessibility label: fix typo

Author: huguesbr

ParseUI/Classes/SignUpViewController/PFSignUpView.m

@@ -36,7 +36,7 @@
 NSString * const PFSignUpViewUsernameFieldAccessibilityIdentifier = @"username";
 NSString * const PFSignUpViewEmailFieldAccessibilityIdentifier = @"email";
 NSString * const PFSignUpViewPasswordFieldAccessibilityIdentifier = @"password";
-NSString * const PFSignUpViewAdditionalFieldAccessibilityIdentifier = @"addtional";
+NSString * const PFSignUpViewAdditionalFieldAccessibilityIdentifier = @"additional";
 NSString * const PFSignUpViewSignUpButtonAccessibilityIdentifier = @"sign up";
 NSString * const PFSignUpViewDismissButtonAccessibilityIdentifier = @"dismiss";