Fix readthedocs build (#1321)

* migrate to new rtd config format and pip

* no type field anymore

* use builtin re for docs

docs/conf.py

@@ -13,7 +13,7 @@
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
 from pathlib import Path
-import regex as re
+import re
 import shutil
 import string
 

docs/environment.yml

@@ -1,10 +0,0 @@
-name: black_docs
-channels:
-  - conda-forge
-dependencies:
-  - python>=3.6
-  - Sphinx==1.7.2
-  - pip:
-      - recommonmark==0.4.0
-      - git+https://git@github.com/psf/black.git
-      - setuptools_scm==3.3.3

docs/requirements.txt

@@ -1,2 +1,3 @@
 recommonmark==0.4.0
 Sphinx==1.7.2
+setuptools_scm==3.3.3

readthedocs.yml

@@ -1,6 +1,5 @@
-name: black
-type: sphinx
-conda:
-  file: docs/environment.yml
+version: 2
 python:
-  version: 3
+  version: 3.8
+  install:
+    - requirements: docs/requirements.txt