Update import paths from github.com/go-gitea to code.gitea.io (#135)

- Update import paths from github.com/go-gitea to code.gitea.io
- Fix import path for travis

See https://docs.travis-ci.com/user/languages/go#Go-Import-Path

vendor/code.gitea.io/git/repo_tree.go

@@ -0,0 +1,26 @@
+// Copyright 2015 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package git
+
+func (repo *Repository) getTree(id sha1) (*Tree, error) {
+	treePath := filepathFromSHA1(repo.Path, id.String())
+	if isFile(treePath) {
+		_, err := NewCommand("ls-tree", id.String()).RunInDir(repo.Path)
+		if err != nil {
+			return nil, ErrNotExist{id.String(), ""}
+		}
+	}
+
+	return NewTree(repo, id), nil
+}
+
+// Find the tree object in the repository.
+func (repo *Repository) GetTree(idStr string) (*Tree, error) {
+	id, err := NewIDFromString(idStr)
+	if err != nil {
+		return nil, err
+	}
+	return repo.getTree(id)
+}