Merge branch 'nga-east-gmm-names' into 'main'

nga-east gmm name changes

See merge request !35

stable-crust/gmm-tree.json

 [
-  { "id": "NGA_EAST_USGS", "weight": 0.667 },
-  { "id": "NGA_EAST_USGS_SEEDS", "weight": 0.333 }
+  { "id": "NGA_EAST_2018", "weight": 0.667 },
+  { "id": "NGA_EAST_SEEDS_2018", "weight": 0.333 }
 ]