patch 8.1.0219: expanding ## fails to escape backtick

Problem:    Expanding ## fails to escape backtick.
Solution:   Escape a backtick in a file name. (closes #3257)
diff --git a/src/version.c b/src/version.c
index cf7fa29..4ea5c75 100644
--- a/src/version.c
+++ b/src/version.c
@@ -799,6 +799,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    219,
+/**/
     218,
 /**/
     217,