Update development environment to latest versions (#102)

* Python 3.8
* dev dependencies
* new-style pre-commit configuration

Author: zupo

.pre-commit-config.yaml

@@ -1,3 +1,4 @@
+repos:
 -   repo: local
     hooks:
     -   id: isort

Pipfile

@@ -7,7 +7,7 @@ name = "pypi"
 pyramid-openapi3 = {editable = true,path = "."}
 
 [dev-packages]
-black = "==19.10b0"
+black = "==20.8b1"
 codespell = "*"
 docutils = "*"
 flake8 = "*"