Fix docs

Author: csm10495

Doc/library/concurrent.futures.rst

@@ -421,7 +421,7 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
       of them the given signal. If the signal is not specified, the default signal
       :data:`signal.SIGTERM` is used.
 
-      After calling this, the caller, should no longer submit tasks to the executor.
+      After calling this, the caller should no longer submit tasks to the executor.
       It is also recommended to still call :meth:`Executor.shutdown` to ensure that all
       other resources associated with the executor are freed.