Jackson2JsonRedisSerializer should allow to customise the JavaType for deserialization via getJavaType()

The Jackson2JsonRedisSerializer has an overridable `getJavaType(Class<?> class)` method, but it does not delegate to this method to determine the `javaType` used by the object mapper when deserializing.

The fix is simple. Instead of setting the private field `JavaType javaType` to the `Class<T> type` passed in from the constructor, it should be set to the type returned by `getJavaType(Class<?> class)`.