Update README: fix broken link

Author: duangsuse

README.md

@@ -1,5 +1,5 @@
 <p align="center">
-<img src="https://raw.githubusercontent.com/pigfromchina/treeToolbox/doc/material-tree.svg" alt="Material Tree Icon">
+<img src="https://github.com/pigfromChina/TreeToolbox/raw/master/doc/material-tree.svg" alt="Material Tree Icon">
 </p>
 
 <h1 align="center">Tree Toolbox</h1>
@@ -22,4 +22,4 @@ directly.
 
 License: __GPL v3__
 
-# Tools [![num](https://img.shields.io/badge/count-0-blue.svg?style=flat-square)](https://github.com/pigfromChina/TreeToolbox/blob/master/app/src/main/assets)
+# Tools [![num](https://img.shields.io/badge/count-0-blue.svg?style=flat-square)](https://github.com/pigfromChina/TreeToolbox/blob/master/app/src/main/assets)