Update version number for next release to 8.6.0. (#694)

Author: jonsimantov

cpp_sdk_version.json

@@ -1,5 +1,5 @@
 {
-  "released": "8.5.0",
-  "stable": "8.5.0",
-  "head": "8.5.0"
+  "released": "8.6.0",
+  "stable": "8.6.0",
+  "head": "8.6.0"
 }

release_build_files/readme.md

@@ -568,7 +568,7 @@ code.
 
 ## Release Notes
 
-### Future Release
+### 8.6.0
 -   Changes
     -   General (Desktop): MacOS SDKs are now built using Xcode 12.2,
         and include support for ARM-based Mac systems.