fix(content): fix minor MD typos on Payment Channel section (#1121)

I've noticed a few typos relating to _italics_ in MD not being interpreted correctly in the payment channel section, which this PR is fixing.

content/systems/filecoin_token/payment_channels/_index.md

@@ -14,7 +14,7 @@ Payment channels are generally used as a mechanism to increase the scalability o
 
 The goal of the Payment Channel Actor specified here is to enable a series of off-chain microtransactions for applications built on top of Filecoin to be reconciled on-chain at a later time with fewer messages that involve the blockchain. Payment channels are already used in the Retrieval Market of the Filecoin Network, but their applicability is not constrained within this use-case only. Hence, here, we provide a detailed description of Payment Channels in the Filecoin network and then describe how Payment Channels are used in the specific case of the Filecoin Retrieval Market.
 
-The payment channel actor can be used to open long-lived, flexible payment channels between users. Filecoin payment channels are _uni-directional_ and can be funded by adding to their balance. Given the context of _uni-directional_ payment channels, we define the **payment channel sender** as the party that receives some service, creates the channel, deposits funds and _sends_ payments (hence the term _payment channel sender_). The *payment channel recipient**, on the other hand is defined as the party that provides services and _receives payment_ for the services delivered (hence the term _payment channel recipient_). The fact that payment channels are uni-directional means that only the payment channel sender can add funds and the recipient can receive funds. Payment channels are identified by a unique address, as is the case with all Filecoin actors.
+The payment channel actor can be used to open long-lived, flexible payment channels between users. Filecoin payment channels are _uni-directional_ and can be funded by adding to their balance. Given the context of _uni-directional_ payment channels, we define the **payment channel sender** as the party that receives some service, creates the channel, deposits funds and _sends_ payments (hence the term _payment channel sender_). The *payment channel recipient*, on the other hand is defined as the party that provides services and *receives payment* for the services delivered (hence the term *payment channel recipient*). The fact that payment channels are uni-directional means that only the payment channel sender can add funds and the recipient can receive funds. Payment channels are identified by a unique address, as is the case with all Filecoin actors.
 
 The payment channel state structure looks like this: