Increase Python minimal supported version to 3.7 because of Tensorflow newer version don't work on Python 3.6

Author: dzrcopilot

.readthedocs.yml

@@ -2,7 +2,7 @@ build:
   image: latest
 
 python:
-  version: 3.6
+  version: 3.7
   setup_py_install: false
 
 requirements_file: requirements-dev.txt

.travis.yml

@@ -70,7 +70,7 @@ that pretty pastes source code.
 
 ## Installation
 
-* Python 3.6+ is required
+* Python 3.7+ is required
 
 * Install the latest stable version:
 

README.md

@@ -91,7 +91,7 @@ Table of contents
 Install Guesslang
 -----------------
 
-Guesslang requires **Python 3.6 or later**.
+Guesslang requires **Python 3.7 or later**.
 
 Install from Pypi
 ^^^^^^^^^^^^^^^^^