Updating to Fable 3 to be able to use Nullable

Author: TheAngryByrd

.config/dotnet-tools.json

@@ -13,6 +13,12 @@
         "commands": [
           "paket"
         ]
-      }
+      },
+    "fable": {
+      "version": "3.1.15",
+      "commands": [
+        "fable"
+      ]
     }
-  }
+  }
+}

.nvmrc

@@ -1 +1 @@
-14.16.1
+16.0.0