Try fixing RTD build of documentation

.readthedocs.yaml

-# .readthedocs.yaml
-# Read the Docs configuration file
-# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
-
-# Required
-version: 2
-
-# Set the version of Python and other tools you might need
-build:
-  os: ubuntu-20.04
-  tools:
-    python: "3.9"
-    # You can also specify other tool versions:
-    # nodejs: "16"
-    # rust: "1.55"
-    # golang: "1.17"
-
-# Build documentation in the docs/ directory with Sphinx
-sphinx:
-   configuration: doc/conf.py
-
-# If using Sphinx, optionally build your docs in additional formats such as PDF
-formats:
-   - pdf
-
-# Optionally declare the Python requirements required to build your docs
-python:
-   install:
-   - requirements: requirements_dev.txt
\ No newline at end of file

requirements_dev.txt

@@ -15,6 +15,6 @@ astroquery>0.4.1
 sep
 photutils
 statsmodels
-esutil
+esutil==0.6.8
 tqdm
 psycopg2