Log Message:
Updated libopus to 1.1.3.

This Opus 1.1.3 release focuses mainly on optimizations and bug
fixes. Changes include:

* Neon optimizations improving performance on ARMv7 and ARMv8 by up to 15%
* Fixes some issues with 16-bit platforms (e.g. TI C55x)
* Fixes to comfort noise generation (CNG)
* Documenting that PLC packets can also be 2 bytes
* Includes experimental ambisonics work (--enable-ambisonics)