Fix typo in comment (#46)
diff --git a/example_test.go b/example_test.go
index 57f8021..329c1cd 100644
--- a/example_test.go
+++ b/example_test.go
@@ -81,7 +81,7 @@
 	}
 
 	st := err.Stacktrace()
-	fmt.Printf("%+v", st[0:2]) // top two framces
+	fmt.Printf("%+v", st[0:2]) // top two frames
 
 	// Output: [github.com/pkg/errors/example_test.go:33 github.com/pkg/errors/example_test.go:78]
 }