Doc update for scala 2.12

Fixes #1058

Author: garyrussell

src/reference/asciidoc/appendix.adoc

@@ -18,38 +18,45 @@ When you use `spring-kafka-test` (version 2.2.x) with the 2.1.x `kafka-clients`
     <groupId>org.springframework.kafka</groupId>
     <artifactId>spring-kafka-test</artifactId>
     <version>${spring.kafka.version}</version>
+    <exclusions>
+        <exclusion>
+            <groupId>org.apache.kafka</groupId>
+            <artifactId>kafka_2.11</artifactId>
+        </exclusion>
+    </exclusions>
     <scope>test</scope>
 </dependency>
 
 <dependency>
     <groupId>org.apache.kafka</groupId>
     <artifactId>kafka-clients</artifactId>
-    <version>2.1.0</version>
+    <version>2.1.1</version>
 </dependency>
 
 <dependency>
     <groupId>org.apache.kafka</groupId>
     <artifactId>kafka-clients</artifactId>
-    <version>2.1.0</version>
+    <version>2.1.1</version>
     <classifier>test</classifier>
 </dependency>
 
 <dependency>
     <groupId>org.apache.kafka</groupId>
     <artifactId>kafka_2.12</artifactId>
-    <version>2.1.0</version>
+    <version>2.1.1</version>
     <scope>test</scope>
 </dependency>
 
 <dependency>
     <groupId>org.apache.kafka</groupId>
     <artifactId>kafka_2.12</artifactId>
-    <version>2.1.0</version>
+    <version>2.1.1</version>
     <classifier>test</classifier>
     <scope>test</scope>
 </dependency>
 ----
 ====
+Note that when switching to scala 2.12 (recommended for 2.1.x and higher), the 2.11 version must be excluded from spring-kafka-test.
 ////
 
 [appendix]