patch 8.1.0415: not actually using 16 colors with vtp

Problem:    Not actually using 16 colors with vtp.
Solution:   Always use 256 colors when vtp is used. (Nobuhiro Takasaki,
            closes #3432)
diff --git a/src/version.c b/src/version.c
index 3ce73b9..637ea99 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    415,
+/**/
     414,
 /**/
     413,