fix: invalid image path

[drumath2237]

Proposed change(s)

I found a image path invalid in docs/installation.md and docs/Learning-Environment-Examples.md

Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)

Types of change(s)

• [ ] Bug fix
• [ ] New feature
• [ ] Code refactor
• [ ] Breaking change
• [x] Documentation update
• [ ] Other (please describe)

Checklist

• [ ] Added tests that prove my fix is effective or that my feature works
• [ ] Updated the changelog (if applicable)
• [x] Updated the documentation (if applicable)
• [ ] Updated the migration guide (if applicable)

Other comments

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