Update js-reporters to 2.1.0

Important changes:

* Mocha 8 and later are now supported. Previously, it's pending tests
  were incorrectly reported as undefined or failing.

* `QUnit.todo()` is now supported. Previously, these intentional
  failures were reported by browserstack-runner as failing tests.

  With js-reported 2.1 the runEnd report counts them as `todo` instead
  of as `failed`.

The API that browserstack-runner depends on has not changed since 1.1.0.
<https://github.com/js-reporters/js-reporters/blob/v2.1.0/CHANGELOG.md>.

Specifically, browserstack-runner captures the following data in
lib/_patch/reporter.js, and proccesses it in lib/server.js under
the "_progress" and "_report" handlers:

* The `testEnd` event, reading:
  - `name` string,
  - `suiteName` string,
  - `status` string,
  - `errors` array.

* The `runEnd` event, reading:
  - `status` string,
  - `testCounts` object with ints `total`, `passed`, `failed`, `skipped`,
  - `runtime` int.

These still exist the same way in the latest release:
<https://github.com/js-reporters/js-reporters/blob/v2.1.0/spec/cri-draft.adoc#runend>

Fixes browserstack#248.
Ref browserstack#247.

package.json

@@ -11,7 +11,7 @@
     "browserstack": "1.3.0",
     "chalk": "0.4.0",
     "circular-json": "0.3.1",
-    "js-reporters": "1.1.0",
+    "js-reporters": "2.1.0",
     "mime": "1.6.0",
     "resolve": "1.1.7",
     "send": "0.16.2",