BIP-0047: Adjust text to match test vectors

The original implementation of BIP-47 in Samourai Wallet reversed
the parameters in the calculation of the HMAC-SHA512 step of
notification transaction blinding.

This change adjusts the text to match the as-implementend behavior
in deployed BIP-47 wallets and the test vectors.

Author: justusranvier

bip-0047.mediawiki

@@ -1,7 +1,7 @@
 RECENT CHANGES:
+* (28 Sep 2017) Adjust text to match test vectors
 * (19 Apr 2016) Define version 2 payment codes
 * (17 Apr 2016) Clarify usage of outpoints in notification transactions
-* (18 Dec 2015) Update explanations to resolve FAQs
 
 <pre>
   BIP: 47
@@ -158,7 +158,7 @@ Note: this procedure is used if Bob uses a version 1 payment code (regardless of
 ## Alice selects the private key corresponding to the designated pubkey: <pre>a</pre>
 ## Alice selects the public key associated with Bob's notification address: <pre>B, where B = bG</pre>
 ## Alice calculates a secret point: <pre>S = aB</pre>
-## Alice calculates a 64 byte blinding factor: <pre>s = HMAC-SHA512(x, o)</pre>
+## Alice calculates a 64 byte blinding factor: <pre>s = HMAC-SHA512(o, x)</pre>
 ### "x" is the x value of the secret point
 ### "o" is the outpoint being spent by the designated input
 # Alice serializes her payment code in binary form.