Bug 1410456 - Update cubeb from upstream to 84e9568. r=achronop

MozReview-Commit-ID: LbKW5KFC37v

--HG--
extra : rebase_source : 83f0a420d9172dfcac47e260cac9675ef8fadc46

media/libcubeb/README_MOZILLA

@@ -5,4 +5,4 @@ Makefile.in build files for the Mozilla build system.
 
 The cubeb git repository is: git://github.com/kinetiknz/cubeb.git
 
-The git commit ID used was 1d53c3a3779cbeb860b16aa38cc7f51e196b9745 (2018-02-13 12:30:46 +1000)
+The git commit ID used was 84e9568141447d13a3f9e03fcff29c2ab6befce1 (2018-02-19 17:50:15 +0200)