Returns code at a given address.
params: [
"0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b",
"0x2", // 2
]
// Result
{
"id":1,
"jsonrpc": "2.0",
"result": "0x600160008035811a818181146012578301005b601b6001356025565b8060005260206000f25b600060078202905091905056"
}