modify error msg

pkg/controller/registry/resolver/resolver.go

@@ -566,7 +566,7 @@ func (r *SatResolver) sortChannel(bundles []*Operator) ([]*Operator, error) {
 		}
 
 	} else if len(headCandidates) < 1 {
-		return nil, fmt.Errorf("Not found the head for channel")
+		return nil, fmt.Errorf("head of channel not found")
 	}
 
 	for _, v := range headCandidates {