Use HashMap::from for immediate-use hashmaps initialization

[shekhirin]

Is your feature request related to a problem? Please describe.
Currently, to initialize a HashMap that's intended to be used immediately with some values, we do

ethers-rs/ethers-etherscan/src/lib.rs

Lines 129 to 131 in 4608ddd

	let mut map = HashMap::new();
	map.insert("guid", guid.as_ref());
	let body = self.create_query("contract", "checkverifystatus", map);

Rust 1.56.0 introduces a new way to do so:

let body = self.create_query("contract", "checkverifystatus", HashMap::from([
    ("guid", guid.as_ref()),
]));

thanks to const generics. Release with that feature is planned to be on 2021-10-21.

Describe the solution you'd like
Replace existing hashmap initializations with proposed solution.