Update bip-0078.mediawiki

Fix a few links.

bip-0078.mediawiki

@@ -64,7 +64,7 @@ Other than that, our proposal is very similar.
 
 In a payjoin payment, the following steps happen:
 
-* The receiver of the payment, presents a [[bip-021.mediawiki|BIP 21 URI]] to the sender with a parameter <code>pj=</code> describing a payjoin endpoint.
+* The receiver of the payment, presents a [[bip-0021.mediawiki|BIP 21 URI]] to the sender with a parameter <code>pj=</code> describing a payjoin endpoint.
 * The sender creates a signed, finalized PSBT with witness UTXO or previous transactions of the inputs. We call this PSBT the <code>original</code>.
 * The receiver replies back with a signed PSBT containing his own signed inputs/outputs and those of the sender. We call this PSBT <code>Payjoin proposal</code>.
 * The sender verifies the proposal, re-signs his inputs and broadcasts the transaction to the Bitcoin network. We call this transaction <code>Payjoin transaction</code>.
@@ -121,7 +121,7 @@ The payjoin proposal MUST NOT:
 
 ===BIP21 payjoin parameters===
 
-This proposal is defining the following new [[bip-021.mediawiki|BIP 21 URI]] parameters:
+This proposal is defining the following new [[bip-0021.mediawiki|BIP 21 URI]] parameters:
 * <code>pj=</code>: Represents an http(s) endpoint which the sender can POST the original PSBT.
 * <code>pjos=0</code>: Signal to the sender that they MUST disallow [[#output-substitution|payment output substitution]]. (See [[#unsecured-payjoin|Unsecured payjoin server]])
 
@@ -665,11 +665,11 @@ A successful exchange with:
 
 ==Backward compatibility==
 
-The receivers are advertising payjoin capabilities through [[https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki|BIP21's URI Scheme]].
+The receivers are advertising payjoin capabilities through [[bip-0021.mediawiki|BIP21's URI Scheme]].
 
 Senders not supporting payjoin will just ignore the <code>pj</code> variable and thus, will proceed to normal payment.
 
 ==Special thanks==
 
 Special thanks to Kukks for developing the initial support to BTCPay Server, to junderw, AdamISZ, lukechilds, ncoelho, nopara73, lontivero, yahiheb, SomberNight, andrewkozlik, instagibbs, RHavar for all the feedback we received since our first implementation.
-Thanks again to RHavar who wrote the [[https://github.com/bitcoin/bips/blob/master/bip-0079.mediawiki|BIP79 Bustapay]] proposal, this gave a good starting point for our proposal.
+Thanks again to RHavar who wrote the [[bip-0079.mediawiki|BIP79 Bustapay]] proposal, this gave a good starting point for our proposal.