Broken `test_bonds` test function in `maps.rs`.

[Sol-Ell]

Its a minor issue, but currently the trait bounds of the T in check_bounds are Send and Send.

http/src/header/map.rs

Lines 3914 to 3918 in 9f86d52

	#[test]
	fn test_bounds() {
	fn check_bounds<T: Send + Send>() {}
	check_bounds::<HeaderMap<()>>();

I think the author of that test meant fn check_bounds<T: Send + Sync> {}.