Remove hyphens from nonce values.

[RFC 5849](http://tools.ietf.org/html/rfc5849#section-3.3) is ambiguous about what characters are allowable in a nonce, but SToPR requires nonce values to be at least 30 alphanumeric characters.

AFOAuth1Client simply uses a UUID4 (random) generator for nonce values. This change removes hyphens so that
`B39A0549-0866-42CA-B26A-F6409850B7FA` becomes `B39A0549-086642CAB26AF6409850B7FA`.