pep-550: Fix a couple of typos (#387)

pep-0550.rst

@@ -330,7 +330,7 @@ compatibility.
 The main reason for why tasks inherit the context, and threads do
 not, is the common usage intent.  Tasks are often used for relatively
 short-running operations which are logically tied to the code that
-spawned the tasks (like running a coroutine with a timeout in
+spawned the task (like running a coroutine with a timeout in
 asyncio).  OS threads, on the other hand, are normally used for
 long-running, logically separate code.
 
@@ -378,7 +378,7 @@ Context variable propagation between tasks::
 
     async def sub():
         # Sleeping will make sub() run after
-        # `var` is modified in main().
+        # "var" is modified in main().
         await asyncio.sleep(1)
 
         # The value of "var" is inherited from main(), but any
@@ -449,7 +449,7 @@ The context variable object has the following methods and attributes:
 
 * ``get(*, topmost=False, default=None)``, if *topmost* is ``False``
   (the default), traverses the execution context top-to-bottom, until
-  the variable value is found, if *topmost* is ``True``, returns
+  the variable value is found.  If *topmost* is ``True``, returns
   the value of the variable in the topmost logical context.
   If the variable value was not found, returns the value of *default*.