use macro for /usr/local/plan9
diff --git a/man/man3/blowfish.3 b/man/man3/blowfish.3
index 5938e35..20d43f6 100644
--- a/man/man3/blowfish.3
+++ b/man/man3/blowfish.3
@@ -38,7 +38,7 @@
 functions take a BFstate structure, a data buffer, and a length, which
 must be a multiple of eight bytes as padding is currently unsupported.
 .SH SOURCE
-.B /usr/local/plan9/src/libsec
+.B \*9/src/libsec
 .SH SEE ALSO
 .IR mp (3),
 .IR aes (3),