Fix typos in the AbstractKafkaHeaderMapper

[artembilan]

No description provided.

[garyrussell]

Travis

> Task :spring-kafka:compileTestJava
/home/travis/build/spring-projects/spring-kafka/spring-kafka/src/test/java/org/springframework/kafka/support/DefaultKafkaHeaderMapperTests.java:158: error: cannot find symbol
		mapper.setRawMappedHaeaders(rawMappedHeaders);
		      ^
  symbol:   method setRawMappedHaeaders(Map<String,Boolean>)
  location: variable mapper of type DefaultKafkaHeaderMapper
/home/travis/build/spring-projects/spring-kafka/spring-kafka/src/test/java/org/springframework/kafka/support/DefaultKafkaHeaderMapperTests.java:183: error: cannot find symbol
		mapper.setRawMappedHaeaders(rawMappedHeaders);
		      ^
  symbol:   method setRawMappedHaeaders(Map<String,Boolean>)
  location: variable mapper of type DefaultKafkaHeaderMapper
/home/travis/build/spring-projects/spring-kafka/spring-kafka/src/test/java/org/springframework/kafka/support/DefaultKafkaHeaderMapperTests.java:211: error: cannot find symbol
		mapper.setRawMappedHaeaders(rawMappedHeaders);
		      ^
  symbol:   method setRawMappedHaeaders(Map<String,Boolean>)
  location: variable mapper of type DefaultKafkaHeaderMapper
3 errors

[artembilan]

Not sure why that has not been committed...

I see something similar for @Nullable in SI WebFluxRequestExecutingMessageHandler.

Will push shortly there.

But this one has been fixed anyway: see latest commit.