Fix utf-16le WHATWG compatibility.
Fix utf-16le WHATWG compatibility.

Per the WHATWG encoding spec, the official name for the utf-16 and
utf-16le labels is utf-16le.

tempbottle/rust-encoding,nox/rust-encoding,tempbottle/rust-encoding,lifthrasiir/rust-encoding,lifthrasiir/rust-encoding,lifthrasiir/rust-encoding,nox/rust-encoding,tempbottle/rust-encoding,nox/rust-encoding