contrib: bump opus from 1.1 to 1.1.2

Should improve performance on all platforms (from http://opus-codec.org) :

* x86 SSE, SSE2 and SSE4.1 intrinsics optimizations with run-time CPU detection contributed by Cisco Systems,
* MIPS intrinsics optimizations contributed by Imagination Technologies,
* ARM Neon optimizations contributed by Linaro and ARM

Tuleap: #407
Change-Id: I3dbd47a89abc7de99132843ff6b899b2b809ab47

contrib/src/opus/SHA512SUMS

-b603efe66d65ef38dbcd0d2bbf213a1d15fa456aee00eca73e99abe4ec78668ed82e661ca7a69e9af4e0bc39e1aa76c4151b7f9840ff621ddcfd69f596cf2ba9  opus-1.1.tar.gz
+12ec6613190a09bf6f300fac70bcf927731b707eae2511cebe7098cb49c4bf43dd21a0af4d22900958636949226df50243c432d53dedeacd46a4978729b5fc0d  opus-1.1.2.tar.gz

contrib/src/opus/rules.mak

 # opus
 
-OPUS_VERSION := 1.1
+OPUS_VERSION := 1.1.2
 
 OPUS_URL := http://downloads.xiph.org/releases/opus/opus-$(OPUS_VERSION).tar.gz