Fixes GetDOMStorageItemsWithParams with correct response type

[bohrium272]

GCD response for GetDOMStorageItems with a 2D array [[key1, value1], [key2, value2]].
This PR changes the type of Entries to [][]string to properly parse this response.

Example:

{
    "command":"DOMStorage.getDOMStorageItems",
    "parameters":{"storageId":{"isLocalStorage":false,"securityOrigin":"https://www.amazon.in"}}
}

{
    "entries": [
        [
            "eelsts",
            "scs"
        ],
        [
            "csmtid",
            "value"
        ],
        [
            "JGKC80APHCXPRJ30YCYC",
            "1"
        ],
        [
            "CSM_previousURL",
            "https://www.amazon.in/"
        ]
    ]
}

[camswords]

@bohrium272, the file changed will be overwritten after ./v2/gcdapigen/build.sh is run. This command regenerates the gcdapi folder based on the downloaded protocol.json file.

getDOMStorageItems in the protocol.json looks correct, it returns an array where each element is an Item. An Item is an array of strings. It seems the gcdapigen.go isn't creating the correct return type given this information.

[camswords]

Closing in preference to #74.