fix: proxy-rewrite.plugin regex_uri support empty value

[liangliang4ward]

Why submit this pull request? proxy-rewrtie.plugin regex_uri support empty value

• [x] Bugfix
• [ ] New feature provided
• [ ] Improve performance
• [ ] Backport patches

What changes will this PR take into?

Please update this section with detailed description. take out regex_uri require=true Related issues

fix/resolve #0001

Checklist:

• [x] Did you explain what problem does this PR solve? Or what new features have been added?
• [x] Have you added corresponding test cases?
• [ ] Have you modified the corresponding document?
• [x] Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first