optimize proguard.

app/proguard-rules.pro

@@ -19,7 +19,5 @@
 # If you keep the line number information, uncomment this to
 # hide the original source file name.
 #-renamesourcefileattribute SourceFile
--keep class nl.rubend.zwemmen.**
 -keep class nl.rubend.zwemmen.** { <fields>; }
 -dontobfuscate
--keepclassmembers class io.ktor.** { volatile <fields>; }