Fix ReadTheDocs

.readthedocs.yml

@@ -5,6 +5,14 @@
 # Required
 version: 2
 
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.7"
+  apt_packages:
+    - plantuml
+    - swig
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
@@ -18,6 +26,5 @@ formats: all
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.7
   install:
-    - requirements: rtd_requirements.txt
+    - requirements: rtd_requirements.txt

rtd_requirements.txt

@@ -1,13 +1,13 @@
 sphinxcontrib-svg2pdfconverter
-sphinx==3.0.3
-breathe==4.19.0
-doc8==0.8.0
-sphinx_rtd_theme==0.4.3
-sphinxcontrib.spelling==5.0.0
+sphinx==4.3.1
+breathe==4.35.0
+doc8==0.10.1
+sphinx_rtd_theme==0.5.2
+sphinxcontrib.spelling==7.2.1
 sphinxcontrib-imagehelper==1.1.1
 colcon-common-extensions==0.2.1
-colcon-mixin==0.1.8
-vcstool==0.2.7
-GitPython==3.1.1
-setuptools==65.5.1
+colcon-mixin==0.2.0
+vcstool==0.3.0
+GitPython==3.1.37
+setuptools==67.6.0
 docutils==0.16.0