chore(deps): update python docker tag to v3.8.2 (GoogleCloudPlatform#3206)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| python | final | patch | `3.8.0b1` -> `3.8.2` |

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trace/cloud-trace-demo-app/app/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.8.0b1
+FROM python:3.8.2
 
 RUN pip3 install --upgrade pip