mark OSMacros.h header private to avoid warning

- Changed OSMacros.h visibility from Public to Private so the header won't be included in the public Headers folder during the build process
- fix warning saying: "umbrella header for module 'OneSignalCore' does not include header 'OSMacros.h'"

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignal.xcodeproj/project.pbxproj

@@ -491,7 +491,7 @@
 		DE7D18C627038249002D3A5D /* OneSignalOutcomes.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = DE7D188027037F43002D3A5D /* OneSignalOutcomes.framework */; };
 		DE7D18CD270385D0002D3A5D /* OSOutcomesRequests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE7D18CB270385D0002D3A5D /* OSOutcomesRequests.m */; };
 		DE7D18CF270385E0002D3A5D /* OSOutcomesRequests.h in Headers */ = {isa = PBXBuildFile; fileRef = DE7D18CE270385E0002D3A5D /* OSOutcomesRequests.h */; };
-		DE7D18D1270389E1002D3A5D /* OSMacros.h in Headers */ = {isa = PBXBuildFile; fileRef = 7AE28B8725B8ADF400529100 /* OSMacros.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		DE7D18D1270389E1002D3A5D /* OSMacros.h in Headers */ = {isa = PBXBuildFile; fileRef = 7AE28B8725B8ADF400529100 /* OSMacros.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		DE7D18D22703ADE0002D3A5D /* OneSignalOutcomes.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = DE7D188027037F43002D3A5D /* OneSignalOutcomes.framework */; };
 		DE7D18D62703B103002D3A5D /* OSInAppMessageOutcome.m in Sources */ = {isa = PBXBuildFile; fileRef = 7A880F2A23FB45FB0081F5E8 /* OSInAppMessageOutcome.m */; };
 		DE7D18D72703B111002D3A5D /* OSInAppMessageOutcome.h in Headers */ = {isa = PBXBuildFile; fileRef = 7A880F2923FB45CE0081F5E8 /* OSInAppMessageOutcome.h */; settings = {ATTRIBUTES = (Public, ); }; };