Fix ambiguous references

instrumentation/kamon-kafka/src/main/scala/kamon/instrumentation/kafka/client/SpanPropagation.scala

@@ -18,11 +18,11 @@ package kamon.instrumentation.kafka.client
 
 import kamon.context.{Context, _}
 import kamon.trace.Span
-import org.apache.kafka.common.header.Headers
+import org.apache.kafka.common.header.{Headers => KafkaHeaders}
 
 import java.nio.charset.StandardCharsets
 
-trait KafkaPropagator extends Propagation.EntryReader[Headers] with Propagation.EntryWriter[Headers] {}
+trait KafkaPropagator extends Propagation.EntryReader[KafkaHeaders] with Propagation.EntryWriter[KafkaHeaders] {}
 
 /**
   * Propagation mechanisms for Kamon's Span data to and from HTTP and Binary mediums.
@@ -33,7 +33,7 @@ object SpanPropagation {
 
     import kamon.trace.SpanPropagation.W3CTraceContext._
 
-    override def read(medium: Headers, context: Context): Context = {
+    override def read(medium: KafkaHeaders, context: Context): Context = {
 
       val contextWithParent = for {
         traceParent <- Option(medium.lastHeader(Headers.TraceParent))
@@ -49,7 +49,7 @@ object SpanPropagation {
       contextWithParent.getOrElse(context)
     }
 
-    override def write(context: Context, medium: Headers): Unit = {
+    override def write(context: Context, medium: KafkaHeaders): Unit = {
       val span = context.get(Span.Key)
 
       if (span != Span.Empty) {
@@ -71,15 +71,15 @@ object SpanPropagation {
 
     import KCtxHeader._
 
-    override def read(medium: Headers, context: Context): Context = {
+    override def read(medium: KafkaHeaders, context: Context): Context = {
       val header = Option(medium.lastHeader(Headers.Kctx))
 
       header.map { h =>
         ContextSerializationHelper.fromByteArray(h.value())
       }.getOrElse(context)
     }
 
-    override def write(context: Context, medium: Headers): Unit = {
+    override def write(context: Context, medium: KafkaHeaders): Unit = {
 
       medium.add(Headers.Kctx, ContextSerializationHelper.toByteArray(context))
     }