Fix incorrect ProGuard rules that allowed shrinking volatile felds

Fixes #1564

Author: dkhalanskyjb

kotlinx-coroutines-core/jvm/resources/META-INF/proguard/coroutines.pro

@@ -3,12 +3,12 @@
 -keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
 
 # Most of volatile fields are updated with AFU and should not be mangled
--keepclassmembernames class kotlinx.** {
+-keepclassmembers class kotlinx.** {
     volatile <fields>;
 }
 
 # Same story for the standard library's SafeContinuation that also uses AtomicReferenceFieldUpdater
--keepclassmembernames class kotlin.coroutines.SafeContinuation {
+-keepclassmembers class kotlin.coroutines.SafeContinuation {
     volatile <fields>;
 }