fix: improve prettyPrint output for `Type` (#90)

Added basic test
diff --git a/lib/src/pretty_print.dart b/lib/src/pretty_print.dart
index 826cad0..4c58f3c 100644
--- a/lib/src/pretty_print.dart
+++ b/lib/src/pretty_print.dart
@@ -107,6 +107,8 @@
           object == null ||
           defaultToString) {
         return value;
+      } else if (object is Type) {
+        return 'instance of `$object`';
       } else {
         return "${_typeName(object)}:$value";
       }
diff --git a/test/pretty_print_test.dart b/test/pretty_print_test.dart
index 0ee73fe..4872850 100644
--- a/test/pretty_print_test.dart
+++ b/test/pretty_print_test.dart
@@ -255,6 +255,10 @@
       expect(prettyPrint(new _PrivateNameIterable()), equals("?:[1, 2, 3]"));
     });
   });
+
+  test('Type', () {
+    expect(prettyPrint(''.runtimeType), 'instance of `String`');
+  });
 }
 
 final _isDart2 = () {