use macro for /usr/local/plan9
diff --git a/man/man3/encode.3 b/man/man3/encode.3
index 44c6afd..fde8296 100644
--- a/man/man3/encode.3
+++ b/man/man3/encode.3
@@ -80,6 +80,6 @@
 
 .EE
 .SH SOURCE
-.B /usr/local/plan9/src/lib9/u32.c
+.B \*9/src/lib9/u32.c
 .br
-.B /usr/local/plan9/src/lib9/u64.c
+.B \*9/src/lib9/u64.c