Fix broken source code links

[jensechu]

💸 TL;DR

Links from docs are broken. (https://developers.reddit.com/docs/examples/apps)

📜 Details

N/A

[Jira] N/A

🧪 Testing Steps / Validation

1. Go to https://developers.reddit.com/docs/examples/apps
2. Verify that each 'Source Code' link goes to a valid github directory.

✅ Checks

• [x] CI tests (if present) are passing
• [x] Adheres to code style for repo
• [x] Contributor License Agreement (CLA) completed if not a Reddit employee