Remove zerver/lib/parallel.py from mypy's exclude_py3.

tools/run-mypy

@@ -49,7 +49,6 @@ zerver/lib/ccache.py
 zerver/lib/debug.py
 zerver/lib/email_mirror.py
 zerver/lib/notifications.py
-zerver/lib/parallel.py
 zerver/lib/tornado_ioloop_logging.py
 zerver/management/commands/create_stream.py
 zerver/management/commands/email-mirror.py

zerver/lib/parallel.py

@@ -28,7 +28,7 @@ def run_parallel(job, data, threads=6):
             except OSError as e:
                 if e.errno != errno.EBADF:
                     raise
-            sys.stdin = open("/dev/null", "r")
+            sys.stdin = open("/dev/null", "r") # type: ignore # py2 and py3 stubs are not compatible
             os._exit(job(item))
 
         pids[pid] = item