fix the bug of convering v0.1 copy resource cfg to v0.2

Consider the following v0.1 cfg:

````
"copy_to_assets" :[
        "../../../main.js"
]
````

in v0.2 it will converts to wrong cfg:

````
   "copy_resources": [
        {
            "from": "../../../main.js", 
            "to": "main.js"
        },
````

the right cfg should be:

````
   "copy_resources": [
        {
            "from": "../../../main.js", 
            "to": ""
        },
````