added chapman and guo vs30 ref

src/main/java/gov/usgs/earthquake/nshmp/gmm/ChapmanGuo_2021.java

@@ -33,6 +33,8 @@ class ChapmanGuo_2021 {
       PGV,
       Imt.mprsImts().toArray(new Imt[0]));
 
+  static final double VS_REF = 590.0;
+
   private static final double[] Z = {
       0.0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8,
       1.0, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, 10.5, 11.5, 12.5 };

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

@@ -216,7 +216,6 @@ final class GroundMotionTables {
     NGA_EAST = initNgaEast();
     NGA_EAST_WEIGHTS = initNgaEastWeights();
     NGA_EAST_SEEDS = initNgaEastSeeds();
-
     KBCG20_EPISTEMIC = initKbcg20();
   }