Drop support for Python3.5

Author: Dominik Gresch

.travis.yml

@@ -1,7 +1,6 @@
 language: python
 cache: pip
 python:
-  - "3.5"
   - "3.6"
   - "3.7"
   - "3.8"

setup.py

@@ -4,8 +4,8 @@
 from setuptools import setup, find_packages
 
 import sys
-if sys.version_info < (3, 5):
-    raise 'must use Python version 3.5 or higher'
+if sys.version_info < (3, 6):
+    raise 'must use Python version 3.6 or higher'
 
 README = r"""Z2Pack is a tool that computes topological invariants and illustrates non-trivial features of Berry curvature. It works as a post-processing tool with all major first-principles codes (z2pack.fp), as well as with tight-binding models (z2pack.tb) and explicit Hamiltonian matrices -- such as the ones obtained from a k.p model (z2pack.hm).
 
@@ -45,12 +45,12 @@
         'fsc.iohelper'
     ],
     extras_require=EXTRAS,
+    python_requires=">=3.6",
     long_description=README,
     classifiers=[
         'License :: OSI Approved :: GNU General Public License v3 (GPLv3)',
         'Natural Language :: English', 'Operating System :: Unix',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',