Documentation: fix a grammatical error in api-builtin.txt

Signed-off-by: Allan Caffee <allan.caffee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: allancaffee

Documentation/technical/api-builtin.txt

@@ -37,7 +37,7 @@ where options is the bitwise-or of:
 
 	Make sure there is a work tree, i.e. the command cannot act
 	on bare repositories.
-	This makes only sense when `RUN_SETUP` is also set.
+	This only makes sense when `RUN_SETUP` is also set.
 
 . Add `builtin-foo.o` to `BUILTIN_OBJS` in `Makefile`.