Clang 4.0 compiler complains in -[MPOAuthCredentialConcreteStore signingKey] method

[nacho4d]

I just compiled the library with new Apple's LLVM Clang 4.0 which complains (shows a warning) in -[MPOAuthCredentialConcreteStore signingKey] method:

/MPOAuth/MPOAuthCredentialConcreteStore.m:183:41: warning: invalid conversion specifier '&' [-Wformat-invalid-specifier]
    return [NSString stringWithFormat:@"%@%&%@", consumerSecret, tokenSecret];
                                          ~^
/MPOAuth/MPOAuthCredentialConcreteStore.m:183:43: warning: more '%' conversions than data arguments [-Wformat]
    return [NSString stringWithFormat:@"%@%&%@", consumerSecret, tokenSecret];

Its result string should be simply: return [NSString stringWithFormat:@"%@&%@", ...]. The & character does not need any kind of escaping or special signs before it ;-)