patch 8.0.0721: :argedit can only have one argument

Problem:    :argedit can only have one argument.
Solution:   Allow for multiple arguments. (Christian Brabandt)
diff --git a/src/version.c b/src/version.c
index 0d5db7f..906e3fa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    721,
+/**/
     720,
 /**/
     719,