added PRVI option

src/main/java/gov/usgs/earthquake/nshmp/gmm/SubductionZone.java

@@ -16,7 +16,9 @@ enum SubductionZone {
 
   @Override
   public String toString() {
-    return Text.enumLabelWithSpaces(this, true);
+    return (this == PRVI)
+        ? name()
+        : Text.enumLabelWithSpaces(this, true);
   }
 
   static enum Type {