fix

doc/canvas.md

 # canvas
 
+[菜鸟教程 - HTML5 <canvas> 参考手册](https://www.runoob.com/tags/ref-canvas.html)
+
 [html：canvas 画布绘图简单入门](https://pengshiyu.blog.csdn.net/article/details/122143631)
 
 [Html5 Canvas 学习笔记](https://oxcow.gitbooks.io/h5-canvas-study-notes/content/)
 
-[CANVAS](https://www.w3cplus.com/blog/tags/604.html)
+[CANVAS](https://www.w3cplus.com/blog/tags/604.html)
\ No newline at end of file