Bump Python requirement to 3.6 from 3.5

This increases the lowest version of Python required to run repo2docker itself.

.github/workflows/test.yml

@@ -78,7 +78,7 @@ jobs:
           - unit
           - venv
         include:
-          - python_version: "3.5"
+          - python_version: "3.6"
             repo_type: venv
 
     steps:

README.md

@@ -16,15 +16,13 @@ For support questions please search or post to https://discourse.jupyter.org/c/b
 See the [contributing guide](CONTRIBUTING.md) for information on contributing to
 repo2docker.
 
-See [our roadmap](https://repo2docker.readthedocs.io/en/latest/contributing/roadmap.html)
-to learn about where the project is heading.
 
 ## Using repo2docker
 ### Prerequisites
 
 1. Docker to build & run the repositories. The [community edition](https://store.docker.com/search?type=edition&offering=community)
    is recommended.
-2. Python 3.5+.
+2. Python 3.6+.
 
 Supported on Linux and macOS. [See documentation note about Windows support.](http://repo2docker.readthedocs.io/en/latest/install.html#note-about-windows-support)
 

docs/source/install.rst

@@ -3,7 +3,7 @@
 Installing ``repo2docker``
 ==========================
 
-repo2docker requires Python 3.5 and above on Linux and macOS. See
+repo2docker requires Python 3.6 or above on Linux and macOS. See
 :ref:`below <windows>` for more information about Windows support.
 
 Prerequisite: Docker

setup.py

@@ -56,7 +56,7 @@ setup(
         "toml",
         "semver",
     ],
-    python_requires=">=3.5",
+    python_requires=">=3.6",
     author="Project Jupyter Contributors",
     author_email="jupyter@googlegroups.com",
     url="https://repo2docker.readthedocs.io/en/latest/",