Fix for #41 and #50

[mtb0x1]

Proposed changes

This PR include a fix for the issues below:

• build: zlib 1.2.13 not available anymore #41
• Curl example doesn't compile : method not found in Option<&NgxStr> #50

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have written my commit messages in the Conventional Commits format.
• I have read the CONTRIBUTING doc
• I have added tests (when possible) that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[ivanitskiy]

@mtb0x1 LGTM. Could you please squash zlib-related commits (0e68c42 and a212649) into one? then I can make a new nginx-sys crate version and upload to crates.io with those fixes.

[mtb0x1]

@ivanitskiy : done.