libvpx: Pull from upstream

Current HEAD: b85ac11737430a7f600ac4efb643d4833afd7428

git log from upstream:
b85ac1173 Release v1.8.0 Northern Shoveler

Test: none
Change-Id: Ib8a95fc530515301c9f6e67970eb35662fbcebca
diff --git a/README.android b/README.android
index 7fc16a6..f7f480e 100644
--- a/README.android
+++ b/README.android
@@ -6,7 +6,7 @@
 
 Date: Wednesday January 16 2019
 Branch: origin/northernshoveler
-Commit: 858fe955ae5a42a0006c974b0837df18b246986f
+Commit: b85ac11737430a7f600ac4efb643d4833afd7428
 
 Description:
 Contains the sources used to compile libvpx.