Add dependencies to setup.py

[austintraver]

Currently, when installing dnsrecon via

pip install 'dnsrecon @ git+https://github.com/darkoperator/dnsrecon@1.1.4'

Invocations of dnsrecon fail if the lxml package is not installed.

This PR updates setup.py to include dnsrecon's required dependencies, in order to ensure it runs successfully when the command is installed in this fashion.

[L1ghtn1ng]

Can you change the install_requires to use the package variable as that should then pull stuff from the requirements.txt

[austintraver]

I couldn't figure out how to do so using the package variable, but I did find a way to pull stuff from the requirements.txt file by adding a line to setup.cfg instead. I tested the installation and can confirm that the dependencies specified in requirements.txt get installed.

[L1ghtn1ng]

Thanks for this