Update ProGuard rules to parse correctly

README.md

@@ -35,7 +35,7 @@ If you are using ProGuard you need to add the following options:
 # Retain generic type information for use by reflection by converters and adapters.
 -keepattributes Signature
 # Retain service method parameters.
--keepclassmembernames,allowobfuscation interface * {
+-keepclassmembers,allowshrinking,allowobfuscation interface * {
     @retrofit2.http.* <methods>;
 }
 # Ignore annotation used for build tooling.