use macro for /usr/local/plan9
diff --git a/man/man3/genrandom.3 b/man/man3/genrandom.3
index 761df86..bb6118c 100644
--- a/man/man3/genrandom.3
+++ b/man/man3/genrandom.3
@@ -38,6 +38,6 @@
 (see
 .IR mp (3)).
 .SH SOURCE
-.B /usr/local/plan9/src/libsec
+.B \*9/src/libsec
 .SH SEE ALSO
 .IR mp (3)