Please fix the copyright notice in the license file

[joshtriplett]

Right now, LICENSE-MIT contains:

Copyright (c) 2016 Itoa Developers

I realize that dtoa and itoa both have the same author; however, this discrepancy (itoa versus dtoa) led to a bit of concern and double-/triple-checking as part of the Debian package review process (which, among many other things, doublechecks licenses).

Given that neither "Dtoa Developers" nor "Itoa Developers" is a legal entity, and copyright is already implicit with or without a notice, please consider just dropping the notice entirely. (See discussions at rust-lang/rust#43498 for details; rustc and similar have already dropped their notices.)

On the other hand, this project is based on the original C++ implementation, and doesn't seem to preserve the license notices from that implementation. The source code does need to preserve the full copyright and license information from the top of dtoa.h, as required by the license of dtoa.h.