patch 8.0.0218: no completion for :cexpr and similar commands

Problem:    No command line completion for :cexpr, :cgetexpr, :caddexpr, etc.
Solution:   Make completion work. (Yegappan Lakshmanan)  Add a test.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    218,
 /**/
     217,
 /**/