docs: fix table render error in env.md

[SF-Zhou]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

Fixed table render error in environment document.

[mention-bot]

@SF-Zhou, thanks for your PR! By analyzing the history of the files in this pull request, we identified @popomore, @huacnlee and @dead-horse to be potential reviewers.

[codecov]

Codecov Report

Merging #619 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #619   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          26     26           
  Lines         633    633           
=====================================
  Hits          633    633

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2296b7b...36ab61b. Read the comment docs.

[fengmk2]

Please fix en too. https://github.com/SF-Zhou/egg/blob/36ab61bae553b63a7ce9df8da77137c4f2d1abc0/docs/source/en/basics/env.md

[dead-horse]

额，没看到评论， @SF-Zhou 可以再提一个 PR 修复英文的