Fix a typo in a comment.
diff --git a/shell.go b/shell.go
index c1613b2..9ec14d3 100644
--- a/shell.go
+++ b/shell.go
@@ -137,7 +137,7 @@
 }
 
 // Split partitions s into fields divided on space, tab, and newline
-// characters.  Single and double quotation marks will be handledn as described
+// characters.  Single and double quotation marks will be handled as described
 // in
 // http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02.
 func Split(s string) []string {