Simplify Ubuntu install instructions

Fixup for b4770bd

Author: kislyuk

README.rst

@@ -33,18 +33,17 @@ Note: SignXML depends on `lxml <https://github.com/lxml/lxml>`_ and `cryptograph
 <https://github.com/pyca/cryptography>`_, which in turn depend on `OpenSSL <https://www.openssl.org/>`_, `LibXML
 <http://xmlsoft.org/>`_, and Python tools to interface with them. You can install those as follows:
 
-+--------------+---------------------------------------------------------------------------------------------+
-| OS           | Command                                                                                     |
-+==============+=============================================================================================+
-| Ubuntu       | ``apt-get install --no-install-recommends python3-pip python3-wheel python3-setuptools``    |
-|              | ``python3-openssl python3-lxml python3-cffi``                                               |
-+--------------+---------------------------------------------------------------------------------------------+
-| Red Hat,     | ``yum install python3-pip python3-pyOpenSSL python3-lxml``                                  |
-| Amazon Linux,|                                                                                             |
-| CentOS       |                                                                                             |
-+--------------+---------------------------------------------------------------------------------------------+
-| Mac OS       | Install `Homebrew <https://brew.sh>`_, then run ``brew install python``.                    |
-+--------------+---------------------------------------------------------------------------------------------+
++--------------+----------------------------------------------------------------------------------------------------------------------+
+| OS           | Command                                                                                                              |
++==============+======================================================================================================================+
+| Ubuntu       | ``apt-get install --no-install-recommends python3-pip python3-wheel python3-setuptools python3-openssl python3-lxml``|
++--------------+----------------------------------------------------------------------------------------------------------------------+
+| Red Hat,     | ``yum install python3-pip python3-pyOpenSSL python3-lxml``                                                           |
+| Amazon Linux,|                                                                                                                      |
+| CentOS       |                                                                                                                      |
++--------------+----------------------------------------------------------------------------------------------------------------------+
+| Mac OS       | Install `Homebrew <https://brew.sh>`_, then run ``brew install python``.                                             |
++--------------+----------------------------------------------------------------------------------------------------------------------+
 
 Synopsis
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