Update vendored tools/.

tools/vendor/github.com/alecthomas/gometalinter/stringset.go

@@ -0,0 +1,29 @@
+package main
+
+type stringSet struct {
+	items map[string]struct{}
+}
+
+func newStringSet(items ...string) *stringSet {
+	setItems := make(map[string]struct{}, len(items))
+	for _, item := range items {
+		setItems[item] = struct{}{}
+	}
+	return &stringSet{items: setItems}
+}
+
+func (s *stringSet) add(item string) {
+	s.items[item] = struct{}{}
+}
+
+func (s *stringSet) asSlice() []string {
+	items := []string{}
+	for item := range s.items {
+		items = append(items, item)
+	}
+	return items
+}
+
+func (s *stringSet) size() int {
+	return len(s.items)
+}