add jackson factory to class initialization

this is due to one of the test classes statically initializing
this factory.

Author: diegomarquezp

google-http-client-jackson2/src/test/resources/META-INF/native-image/com.google.http-client/google-http-client-jackson2/native-image.properties

@@ -1,5 +1,6 @@
 Args=--initialize-at-build-time=com.google.api.client.json.jackson2.JacksonFactoryTest \
 --initialize-at-build-time=com.google.api.client.json.jackson2.JacksonGeneratorTest \
+--initialize-at-build-time=com.google.api.client.json.jackson2.JacksonFactory \
 --initialize-at-build-time=com.google.api.client.util.StringUtils \
 --initialize-at-build-time=com.fasterxml.jackson.core \
 --initialize-at-build-time=org.junit.runner.RunWith,java.lang.annotation.Annotation