patch 8.1.0087: v:shell_error is always zero when using terminal for "!cmd"

Problem:    v:shell_error is always zero when using terminal for "!cmd".
Solution:   Use "exitval" of terminal-job. (Ozaki Kiichi, closes #2994)
diff --git a/src/version.c b/src/version.c
index bd3bca1..72a8238 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    87,
+/**/
     86,
 /**/
     85,