use macro for /usr/local/plan9
diff --git a/man/man4/9pserve.4 b/man/man4/9pserve.4
index 81cfc26..510c16e 100644
--- a/man/man4/9pserve.4
+++ b/man/man4/9pserve.4
@@ -43,4 +43,4 @@
 .IR intro (4),
 .IR intro (9p)
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/9pserve.c
+.B \*9/src/cmd/9pserve.c