Use simple quote for Vundle Plugin

Otherwise you get :
```shell
Error detected while processing /home/n3b/.vimrc:
line   20:
E471: Argument required: Plugin
Press ENTER or type command to continue
```

Author: benoittgt

README.md

@@ -16,7 +16,7 @@ Using [Vundle](https://github.com/gmarik/vundle)
 
 ```VimL
 
-    Plugin "sudar/vim-arduino-syntax"
+    Plugin 'sudar/vim-arduino-syntax'
 
     And :PluginInstall