~ Python requirements bumped to 3.6 (slixmpp does not compile on 3.5 anymore)

.travis.yml

@@ -1,6 +1,5 @@
 language: python
 python:               # this works for Linux but is ignored on macOS or Windows
-  - "3.5"
   - "3.6"
   - "3.7"
   - "3.8"

README.md

@@ -45,7 +45,7 @@ The bots can be installed and run at your choice from :
 
 A classic (Python package) installation requires :
 
-- Python 3 (>= 3.5) and pip ([should already be bundled with Python](https://pip.pypa.io/en/stable/installing)) ; e.g. on Debian : `sudo apt install python3 python3-pip`
+- Python 3 (>= 3.6) and pip ([should already be bundled with Python](https://pip.pypa.io/en/stable/installing)) ; e.g. on Debian : `sudo apt install python3 python3-pip`
 - [signal-cli](https://github.com/AsamK/signal-cli) for the *Signal* backend (see [Using the Signal backend](#using-the-signal-backend) below for requirements)
 - For *transbot* : an IBM Cloud account ([free account ok](https://www.ibm.com/cloud/free))
 

setup.py

@@ -103,7 +103,8 @@ setuptools.setup(
         'Topic :: Software Development :: Internationalization'
     ],
     # PyYAML requires Python 3.5+
-    python_requires='>=3.5',
+    # slixmpp 1.7.0+ requires Python 3.7 (but still compiles on 3.6)
+    python_requires='>=3.6',
     # TODO This duplicates requirements-build.txt ?
     setup_requires=['setuptools-scm'],
     # TODO This duplicates requirements-runtime.txt