pep-492: Use backticks

pep-0492.txt

@@ -30,7 +30,7 @@ This PEP assumes that the asynchronous tasks are scheduled and
 coordinated by an Event Loop similar to that of stdlib module
 ``asyncio.events.AbstractEventLoop``.  While the PEP is not tied to any
 specific Event Loop implementation, it is relevant only to the kind of
-coroutine that uses "yield" as a signal to the scheduler, indicating
+coroutine that uses ``yield`` as a signal to the scheduler, indicating
 that the coroutine will be waiting until an event (such as IO) is
 completed.