missed one part of fix, added import

Author: cowtowncoder

ion/src/main/java/tools/jackson/dataformat/ion/EnumAsIonSymbolSerializer.java

@@ -18,6 +18,7 @@
 import tools.jackson.core.exc.StreamWriteException;
 
 import tools.jackson.databind.*;
+import tools.jackson.databind.cfg.EnumFeature;
 import tools.jackson.databind.jsonFormatVisitors.JsonFormatVisitorWrapper;
 import tools.jackson.databind.ser.std.StdScalarSerializer;