Fix Read the Docs build (#214)

* Change requirements.txt

* Fix typo in requirements.txt

requirements.txt

@@ -1,13 +1,12 @@
 git+https://github.com/simphony/osp-core.git#egg=osp-core
-ipython==8.1.1
-jinja2==3.0.3
-jupyter==1.0.0
-markupsafe==2.1.1
-myst-parser==0.17.0
-nbsphinx==0.8.8
-sphinx==4.4.0
+jinja2 >= 3.0.3, < 4
+jupyter >= 1.0.0, < 2
+markupsafe >= 2.1.1, < 3
+myst-parser >= 0.18.0, < 0.19
+nbsphinx >= 0.8.9, < 0.9
+sphinx >= 4.4.0, < 5
 sphinx-autobuild==2021.3.14
-sphinx_book_theme==0.2.0
-sphinxcontrib-plantuml==0.23
-sphinx-copybutton==0.5.0
-sphinx-panels==0.6.0
+sphinx_book_theme >= 0.3.2, < 0.4
+sphinxcontrib-plantuml >= 0.24, < 0.25
+sphinx-copybutton >= 0.5.0, < 0.6
+sphinx-panels >= 0.6.0, < 0.7