Update Proguard rules for D8
-# Retain generic type information for use by reflection by converters and adapters.
--keepattributes Signature
+# Retrofit does reflection on generic parameters and InnerClass is required to use Signature.
+-keepattributes Signature, InnerClasses
# Retain service method parameters when optimizing.
-keepclassmembers,allowshrinking,allowobfuscation interface * {
