fix(core): apply staticDirectories to base webpack config

[Josh-Cena]

Motivation

Missed this in #4095

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

N/A ¯_(ツ)_/¯ Wonder how we should test this though

[netlify]

✔️ [V2]

🔨 Explore the source changes: 06f9324

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61966858ec486b0008dfa0da

😎 Browse the preview: https://deploy-preview-5965--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟢 Performance	95
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-5965--docusaurus-2.netlify.app/

[github-actions]

Size Change: -1 B (0%)

Total Size: 891 kB

ℹ️ View Unchanged

Filename	Size	Change
website/.docusaurus/globalData.json	38.3 kB	0 B
website/build/assets/css/styles.********.css	100 kB	0 B
website/build/assets/js/main.********.js	477 kB	0 B
website/build/blog/2017/12/14/introducing-docusaurus/index.html	66.1 kB	0 B
website/build/blog/index.html	36.8 kB	0 B
website/build/docs/index.html	44 kB	+1 B (0%)
website/build/docs/installation/index.html	51.7 kB	-2 B (0%)
website/build/index.html	29.5 kB	0 B
website/build/tests/docs/index.html	25.2 kB	0 B
website/build/tests/docs/standalone/index.html	21.7 kB	0 B

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