patch 9.1.0239: filetype: gnuplot history files are not recognised

Problem:  filetype: gnuplot history files are not recognised
Solution: detect .gnuplot_history files as gnuplot
          (Wu, Zhenyu)

closes: #14360

Signed-off-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index b1844bf..e05ab84 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    239,
+/**/
     238,
 /**/
     237,