fix(deps): update dependency @opencensus/propagation-stackdriver to v…

…0.0.21 (#1227)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [@opencensus/propagation-stackdriver](https://togithub.com/census-instrumentation/opencensus-node) | dependencies | patch | [`0.0.20` -> `0.0.21`](https://renovatebot.com/diffs/npm/@opencensus%2fpropagation-stackdriver/0.0.20/0.0.21) |

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### Release Notes

<details>
<summary>census-instrumentation/opencensus-node</summary>

### [`v0.0.21`](https://togithub.com/census-instrumentation/opencensus-node/blob/master/CHANGELOG.md#&#8203;0021---2020-03-30)

[Compare Source](https://togithub.com/census-instrumentation/opencensus-node/compare/v0.0.20...v0.0.21)

-   chore(core): store cls contexts on a Map ([#&#8203;786](https://togithub.com/census-instrumentation/opencensus-node/issues/786))
-   fix: `opencensus-instrumentation-grpc` reduce vulnerabilities ([#&#8203;749](https://togithub.com/census-instrumentation/opencensus-node/issues/749))

</details>

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package.json

@@ -99,7 +99,7 @@
   },
   "dependencies": {
     "@google-cloud/common": "^2.0.0",
-    "@opencensus/propagation-stackdriver": "0.0.20",
+    "@opencensus/propagation-stackdriver": "0.0.21",
     "builtin-modules": "^3.0.0",
     "console-log-level": "^1.4.0",
     "continuation-local-storage": "^3.2.1",