Restore install_requires using requirements.txt

Author: laurentpellegrino

setup.py

@@ -5,6 +5,9 @@
 with open("README.md", "r") as fh:
     long_description = fh.read()
 
+with open('requirements.txt') as f:
+    requirements = f.read().splitlines()
+
 setuptools.setup(
     name="ipregistry",
     version=__version__,
@@ -14,6 +17,7 @@
     long_description=long_description,
     long_description_content_type="text/markdown",
     url="https://github.com/ipregistry/ipregistry-python",
+    install_requires=requirements,
     packages=setuptools.find_packages(),
     classifiers=[
         "Programming Language :: Python :: 2",