patch 8.0.1606: singular/plural variants not translated

Problem:    Singular/plural variants not translated.
Solution:   Add NGETTEXT argument to xgettext. (Sergey Alyoshin)
diff --git a/src/version.c b/src/version.c
index 3236096..4531c82 100644
--- a/src/version.c
+++ b/src/version.c
@@ -767,6 +767,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1606,
+/**/
     1605,
 /**/
     1604,