use macro for /usr/local/plan9
diff --git a/man/man3/string.3 b/man/man3/string.3
index 0b39d5c..e17906b 100644
--- a/man/man3/string.3
+++ b/man/man3/string.3
@@ -266,6 +266,6 @@
 has been read.
 The input stack has a maximum depth of 32 nested include files.
 .SH SOURCE
-.B /usr/local/plan9/src/libString
+.B \*9/src/libString
 .SH SEE ALSO
 .IR bio (3)