fix readthedocs compilation

docs/requirements.txt

@@ -1,13 +1,27 @@
-alabaster==0.7.10
-Babel==2.4.0
-docutils==0.13.1
-imagesize==0.7.1
-Jinja2==2.10.1
-MarkupSafe==1.0
-Pygments==2.2.0
-pytz==2017.2
-requests==2.20.0
-six==1.10.0
-snowballstemmer==1.2.1
-Sphinx==1.3.6
-git+https://github.com/fabpot/sphinx-php.git@7312eccce9465640752e51373a480da700e02345#egg_name=sphinx-php
+alabaster==0.7.12
+Babel==2.9.0
+certifi==2020.12.5
+chardet==4.0.0
+docutils==0.16
+idna==2.10
+imagesize==1.2.0
+Jinja2==2.11.3
+MarkupSafe==1.1.1
+packaging==20.9
+pkg-resources==0.0.0
+Pygments==2.8.1
+pyparsing==2.4.7
+pytz==2021.1
+requests==2.25.1
+six==1.15.0
+snowballstemmer==2.1.0
+Sphinx==3.5.3
+sphinx-php==1.0
+sphinx-rtd-theme==0.5.1
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+urllib3==1.26.4