Examples: Downgraded Xcode project object version (50->48) to support Xcode 9.2 (last version supported on macOS 10.12) (#2133, #1929)

examples/example_apple_opengl2/example_apple_opengl2.xcodeproj/project.pbxproj

@@ -3,7 +3,7 @@
 	archiveVersion = 1;
 	classes = {
 	};
-	objectVersion = 50;
+	objectVersion = 48;
 	objects = {
 
 /* Begin PBXBuildFile section */