fix spelling mistake

diff --git a/walk.go b/walk.go
index 54baee4..36541c9 100644
--- a/walk.go
+++ b/walk.go

@@ -8,7 +8,7 @@
 )
 
 // Walker provides a convenient interface for iterating over the
-// descendents of a filesystem path.
+// descendants of a filesystem path.
 // Successive calls to the Step method will step through each
 // file or directory in the tree, including the root. The files
 // are walked in lexical order, which makes the output deterministic