patch 8.1.1870: using :pedit from a help file sets help filetype

Problem:    Using :pedit from a help file sets the preview window to help
            filetype. (Wang Shidong)
Solution:   Do not set "keep_help_flag". (closes #3536)
diff --git a/src/version.c b/src/version.c
index cb59ef0..8e2ac30 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1870,
+/**/
     1869,
 /**/
     1868,