use macro for /usr/local/plan9
diff --git a/man/man3/bin.3 b/man/man3/bin.3
index 1d1e320..7606202 100644
--- a/man/man3/bin.3
+++ b/man/man3/bin.3
@@ -89,7 +89,7 @@
 upon a call to
 .IR binfree .
 .SH SOURCE
-.B /usr/local/plan9/src/libbin
+.B \*9/src/libbin
 .SH SEE ALSO
 .IR malloc (3)
 .SH DIAGNOSTICS