add nshm to gson

src/lib/src/main/java/gov/usgs/earthquake/nshmp/netcdf/www/NetcdfWsUtils.java

@@ -11,6 +11,7 @@ import com.google.gson.GsonBuilder;
 
 import gov.usgs.earthquake.nshmp.gmm.Imt;
 import gov.usgs.earthquake.nshmp.netcdf.NetcdfVersion;
+import gov.usgs.earthquake.nshmp.netcdf.Nshm;
 import gov.usgs.earthquake.nshmp.www.ResponseBody;
 import gov.usgs.earthquake.nshmp.www.ResponseMetadata;
 import gov.usgs.earthquake.nshmp.www.WsUtils.EnumSerializer;
@@ -27,6 +28,7 @@ public class NetcdfWsUtils {
   static {
     GSON = new GsonBuilder()
         .registerTypeAdapter(Imt.class, new EnumSerializer<Imt>())
+        .registerTypeAdapter(Nshm.class, new EnumSerializer<Nshm>())
         .registerTypeAdapter(Double.class, new NaNSerializer())
         .disableHtmlEscaping()
         .serializeNulls()