Bump heapsize to at least 0.4.1 (relicensed)
Bump heapsize to at least 0.4.1 (relicensed)

Heapsize was released as `0.4.1` to reflect the license change. (https://github.com/servo/heapsize/pull/85).

Fixes https://github.com/servo/rust-url/issues/317.
servo/rust-url,servo/rust-url