setup: add python_requires='>=3.5' (#723)

.travis.yml

@@ -1,6 +1,5 @@
 language: python
 sudo: false
-python:
   - "3.6"
 install:
   - "pip install -r dev-requirements.txt"

setup.py

@@ -12,9 +12,12 @@ setup(name="i3pystatus",
           "Environment :: X11 Applications",
           "License :: OSI Approved :: MIT License",
           "Operating System :: POSIX :: Linux",
-          "Programming Language :: Python :: 3",
+          "Programming Language :: Python :: 3.5",
+          "Programming Language :: Python :: 3.6",
+          "Programming Language :: Python :: 3.7",
           "Topic :: Desktop Environment :: Window Managers",
       ],
+      python_requires='>=3.5',
       packages=find_packages(include=['i3pystatus', 'i3pystatus.*']),
       entry_points={
           "console_scripts": [