fix test and use latest coveralls tool

.config/dotnet-tools.json

@@ -7,6 +7,12 @@
       "commands": [
         "dotnet-cake"
       ]
+    },
+    "coveralls.net": {
+      "version": "3.0.0",
+      "commands": [
+        "csmacnz.Coveralls"
+      ]
     }
   }
 }