recon-ng: Specify libxml2 and libxslt as dependencies to fix the build
recon-ng: Specify libxml2 and libxslt as dependencies to fix the build

- Before (issue 12651), this formula would fail to `pip install lxml`, a
  dependency, with a build error that was hard to decipher. From the pip logs,
  this failure was due to libxml2 and libxslt being missing.
- This installs them via `depends_on` for non-MacOS, and `recon-ng`
  installs and runs successfully.

Closes #13266.

Signed-off-by: Michka Popoff <7b0496f66f66ee22a38826c310c38b415671b832@gmail.com>

maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core