Fix no response logging on async Feign (#1450)

* Fix no response logging on async Feign.

Copy log level onto asyncBuilder as well as setting it on the builder, so responses get logged in the asynchronous case.

* Forgot a semicolon

* Run license:format; make logLevel not final.

Co-authored-by: Andrew Winterman <andrew.winterman@altruist.com>

core/src/main/java/feign/AsyncFeign.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2012-2020 The Feign Authors
+ * Copyright 2012-2021 The Feign Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -63,7 +63,7 @@ public static class AsyncBuilder<C> {
     private Supplier<C> defaultContextSupplier = () -> null;
     private AsyncClient<C> client;
 
-    private final Logger.Level logLevel = Logger.Level.NONE;
+    private Logger.Level logLevel = Logger.Level.NONE;
     private final Logger logger = new NoOpLogger();
 
     private Decoder decoder = new Decoder.Default();
@@ -159,6 +159,7 @@ public AsyncFeign<C> build() {
      */
     public AsyncBuilder<C> logLevel(Logger.Level logLevel) {
       builder.logLevel(logLevel);
+      this.logLevel = logLevel;
       return this;
     }