updated for version 7.4.423

Problem:    expand("$shell") does not work as documented.
Solution:   Do not escape the $ when expanding environment variables.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    423,
 /**/
     422,
 /**/