setup: remove 'future' and 'tests_require'

* 'future' not needed after dropping Python 2 support.
* Remove deprecated 'tests_requires'.
* Replace python_requires = '~=3.6', with '>=3.6' (same but clearer).

Author: GraemeWatt

hepdata_converter_ws_client/__init__.py

@@ -8,7 +8,6 @@
 import shutil
 from io import BytesIO
 from builtins import str as text
-from future.utils import raise_from
 
 __author__ = 'Michał Szostak'
 
@@ -89,7 +88,7 @@ def convert(url, input, output=None, options={}, id=None, extract=True, timeout=
             r.raise_for_status()
     except requests.RequestException as e:
         # We get here from a timeout as well as a non-500 error code
-        raise_from(Error('Request to %s failed' % url), e)
+        raise Error('Request to %s failed' % url) from e
 
     error_occurred = False
     try:

setup.py

@@ -26,12 +26,10 @@ def get_version():
 setup(
     name='hepdata-converter-ws-client',
     version=get_version(),
-    python_requires = '~=3.6',
+    python_requires = '>=3.6',
     install_requires=[
-        'future>=0.18.2',
         'requests>=2.23.0',
     ],
-    tests_require=test_requirements,
     extras_require=extras_require,
     packages=['hepdata_converter_ws_client'],
     url='https://github.com/HEPData/hepdata-converter-ws-client',