net: fix typo in comment

Change-Id: I8b2063e65d3454a694a789c1682dacfe0bea2e19
Reviewed-on: https://go-review.googlesource.com/8965
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/net/fd_plan9.go b/src/net/fd_plan9.go
index ddadb6e..38355e2 100644
--- a/src/net/fd_plan9.go
+++ b/src/net/fd_plan9.go
@@ -11,7 +11,7 @@
 	"time"
 )
 
-// Network file descritor.
+// Network file descriptor.
 type netFD struct {
 	// locking/lifetime of sysfd + serialize access to Read and Write methods
 	fdmu fdMutex