Update add.go for fixing the test failed by using submodules.

If the repository is submodule, `.git` will be a file to indicate `.git` directory.

Makefile

@@ -22,6 +22,7 @@ test:
 
 update: setup
 	dep ensure
+	git submodule update --init
 
 lint: setup
 	go vet $$(go list ./... | grep -v vendor)

add/add.go

@@ -18,13 +18,9 @@ func (add *AddCommand) isExistAndGitRepository(absPath string, path string) erro
 		return fmt.Errorf("%s: not directory", path)
 	}
 	fmode, err = os.Stat(filepath.Join(absPath, ".git"))
-	fmt.Printf(filepath.Join(absPath, ".git"))
-	if err != nil || !fmode.IsDir() {
-		if err != nil {
-			fmt.Printf("Error: %s\n", err.Error())
-		}
-		fmt.Printf("%s: not git repository (%v)", absPath, fmode.Mode())
-		return fmt.Errorf("%s: not git repository (%v)", path, fmode.Mode())
+	// If the repository of path is submodule, `.git` will be a file to indicate the `.git` directory.
+	if os.IsNotExist(err) {
+		return fmt.Errorf("%s: not git repository", path)
 	}
 	return nil
 }