setup.py: there's currently an issue with RTDs sidebar when using sph…

…inx-rtd-theme == 0.3.0 (see readthedocs/readthedocs.org#3925)

setup.py

@@ -37,7 +37,7 @@
                       'numpy>=1.7',
                       'scipy>=1.0.0'
                       'sphinx>=1.7.2'
-                      'sphinx-rtd-theme>=0.3.0'],
+                      'sphinx-rtd-theme<0.3.0'],
     python_requires='>=3.5',
     zip_safe=False,
     include_package_data=True