fix pypi link

Author: VarIr

docs/user/installation.rst

@@ -47,7 +47,7 @@ Stable Hub Toolbox release
 ==========================
 
 Stable releases of the Hub Toolbox are added to 
-`PyPI <https://pypi.python.org/pypi/hub-toolbox>`_.
+`PyPI <https://pypi.python.org/pypi/hub-toolbox>`_ .
 To install the latest stable release, simply use `pip` 
 (you may need to install it first via your operating system's package manager,
 e.g. ``sudo apt install python3-pip``).