Fix compilation error due to missing import of Version

Author: dakrone

core/src/main/java/org/elasticsearch/index/mapper/IpFieldMapper.java

@@ -31,6 +31,7 @@
 import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.BytesRef;
+import org.elasticsearch.Version;
 import org.elasticsearch.action.fieldstats.FieldStats;
 import org.elasticsearch.common.Explicit;
 import org.elasticsearch.common.Nullable;