Notify should allow Obj Params

[sampaioletti]

I can't find in the json-rpc 2.0 spec where a notify params can't be objects. Current implementation only allows null or array.

jsonrpc/core-client/transports/src/lib.rs

Lines 298 to 307 in 38af3c9

	pub fn notify<T: Serialize>(&self, method: &str, args: T) -> RpcResult<()> {
	let args =
	serde_json::to_value(args).expect("Only types with infallible serialisation can be used for JSON-RPC");
	let params = match args {
	Value::Array(vec) => Params::Array(vec),
	Value::Null => Params::None,
	_ => {
	return Err(RpcError::Client(
	"RPC params should serialize to a JSON array, or null".into(),
	))

I believe it should implement the same logic as the call_method implementation above it

jsonrpc/core-client/transports/src/lib.rs

Lines 269 to 284 in 38af3c9

	pub fn call_method<T: Serialize, R: DeserializeOwned>(
	&self,
	method: &str,
	returns: &str,
	args: T,
	) -> impl Future<Output = RpcResult<R>> {
	let returns = returns.to_owned();
	let args =
	serde_json::to_value(args).expect("Only types with infallible serialisation can be used for JSON-RPC");
	let params = match args {
	Value::Array(vec) => Ok(Params::Array(vec)),
	Value::Null => Ok(Params::None),
	Value::Object(map) => Ok(Params::Map(map)),
	_ => Err(RpcError::Client(
	"RPC params should serialize to a JSON array, JSON object or null".into(),
	)),

I can do a PR if I'm correct in my research.

Wonderful project. Thank you.