Refactor duplicate function and renamed gas option type

[suraneti]

reduceOption function is declared in both getRate and getRateAmountOut function, so it would be better if changed to a class method.

const reduceOption = (option: any) => {
	return {
		gasLimit: option.gasLimit,
		gasPrice: `${this.web3.utils.toWei(option.gasPrice, "gwei")}`
	}
}

Change to a private class method.

private getGasOption(option: TradeOption): GasOption {
	return {
		gasLimit: `${option.gasLimit}`,
		gasPrice: `${this.web3.utils.toWei(option.gasPrice, "gwei")}`
	}
}

And I also changed the type name from Options to GasOption in types/Web3.ts for better understanding, no idea this is good or not.