Release notes format fixes for platform series (#1053)

* add spaces in platform series

* removed mac OS 32 bit

Author: DellaBitta

release_build_files/readme.md

@@ -640,14 +640,14 @@ code.
       cause duplicate symbol linker errors in conjunction with other libraries
       ([#989](https://github.com/firebase/firebase-cpp-sdk/issues/989)).
     - GMA (iOS): Updated iOS dependency to Google Mobile Ads SDK version 9.7.0.
-    - General (Android,iOS,Linux,macOS 32-bit): Fixed an integer overflow which
+    - General (Android, iOS, Linux 32-bit): Fixed an integer overflow which
       could result in a crash or premature return when waiting for a `Future`
       with a timeout
       ([#1042](https://github.com/firebase/firebase-cpp-sdk/pull/1042)).
 
 ### 9.3.0
 -   Changes
-    - General (Android,Linux): Fixed a concurrency bug where waiting for an
+    - General (Android, Linux): Fixed a concurrency bug where waiting for an
       event with a timeout could occasionally return prematurely, as if the
       timeout had occurred
       ([#1021](https://github.com/firebase/firebase-cpp-sdk/pull/1021)).