Upgrade Xargo to v0.3.22

This includes a “Fix for changed rustc directory layout.” change:
https://github.com/japaric/xargo/blob/master/CHANGELOG.md#v0322---2020-07-29

We use Xargo to compile rust-std for Windows UWP targets.
I built `xargo.exe` on Taskcluster with task
https://community-tc.services.mozilla.com/tasks/IHwGq_ViRpGuomBx82XmpQ
created through https://community-tc.services.mozilla.com/tasks/create
with this definition:

```yaml
provisionerId: proj-servo
workerType: win2016
schedulerId: taskcluster-github
created: '2021-01-25T19:39:29.952Z'
deadline: '2021-01-26T19:39:29.952Z'
expires: '2022-01-25T19:39:29.952Z'
payload:
  mounts:
    - file: rustup-init.exe
      content:
        url: https://win.rustup.rs/x86_64
  command:
    - '%HOMEDRIVE%%HOMEPATH%\rustup-init.exe --profile=minimal -y'
    - set PATH=%HOMEDRIVE%%HOMEPATH%\.cargo\bin;%PATH%
    - |-
      cargo install xargo --version 0.3.22
      copy %HOMEDRIVE%%HOMEPATH%\.cargo\bin\xargo.exe .
  artifacts:
    - name: public/xargo.exe
      path: xargo.exe
      type: file
      expires: '2022-01-25T15:07:23.782706Z'
  maxRunTime: 5400
metadata:
  name: Xargo build for Windows
  description: ''
  owner: infra@servo.org
  source: https://community-tc.services.mozilla.com/tasks/create
```

(Note the "update timestamps" button in the bottom-right menu.)

I then created a ZIP file that contains `xargo-v0.3.22/xargo.exe` and
uploaded it with `aws s3 cp ./xargo-v0.3.22.zip s3://servo-deps-2/msvc-deps/`
where our build system can find it.

python/servo/packages.py

@@ -11,5 +11,5 @@ WINDOWS_MSVC = {
     "openssl": "111.3.0+1.1.1c-vs2017-2019-09-18",
     "gstreamer-uwp": "1.16.0.5",
     "openxr-loader-uwp": "1.0",
-    "xargo": "v0.3.17",
+    "xargo": "v0.3.22",
 }