patch 8.0.0957: a terminal job can deadlock when sending many keys

Problem:    When term_sendkeys() sends many keys it may get stuck in writing
            to the job.
Solution:   Make the write non-blocking, buffer keys to be sent.

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    957,
 /**/
     956,
 /**/