fix typo

gbvendor/manifest_test.go

diff --git a/gbvendor/manifest_test.go b/gbvendor/manifest_test.go
index 98a44cb..aa486e5 100644
--- a/gbvendor/manifest_test.go
+++ b/gbvendor/manifest_test.go
@@ -37,7 +37,7 @@
 
 	mf := filepath.Join(root, "vendor")
 
-	// check that reading an non existant manifest
+	// check that reading an nonexistent manifest
 	// does not return an error
 	m, err := ReadManifest(mf)
 	if err != nil {