It’s a problem with old Proguard. Your Proguard version is 4.7 but you need version 5.0 or above. You have probably old NVIDIA CodeWorks installed. You should install version 1R6u1 which is attached to UE 4.16. Please notice that version 1R6 is wrong, it should be exactly 1R6u1. It’s located under path /Engine/Extras/AndroidWorks/.
You could alternatively download the newest ProGuard from this website: ProGuard Java Optimizer and Obfuscator - Browse /proguard/5.3 at SourceForge.net and replace under path: /NVPACK/android-sdk-windows/tools/proguard