Fix example 87 in Spring's R2dbc reference documentation

[jsattler]

The "Example 87. @configuration class to configure R2DBC mapping support" contains the following example, which seems to be wrong:

...
@Override
protected List<Object> getCustomConverters() {

  List<Converter<?, ?>> converterList = new ArrayList<Converter<?, ?>>();
  converterList.add(new org.springframework.data.r2dbc.test.PersonReadConverter());
  converterList.add(new org.springframework.data.r2dbc.test.PersonWriteConverter());
  return converterList;
}

Results in:

• Required type: List<Object>
• Provided type: List<Converter<?,?>>

While looking at this example, I was also wondering why we cannot inject the Converters instead of creating them within the getCustomConverters() method.

[schauder]

Fixed by f5989e1