Remove outdated references to Python 2.7 in docs

docs/install.rst

@@ -1,8 +1,7 @@
 Installing Pelican
 ##################
 
-Pelican currently runs best on Python 2.7.x and 3.5+; earlier versions of
-Python are not supported.
+Pelican currently runs best on 3.6+; earlier versions of Python are not supported.
 
 You can install Pelican via several different methods. The simplest is via
 `pip <https://pip.pypa.io/en/stable/>`_::
@@ -75,7 +74,6 @@ automatically installed without any action on your part:
   broadcast signaling system
 * `unidecode <https://pypi.org/project/Unidecode/>`_, for ASCII
   transliterations of Unicode text
-* `six <https://pypi.org/project/six/>`_,  for Python 2 and 3 compatibility
   utilities
 * `MarkupSafe <https://pypi.org/project/MarkupSafe/>`_, for a markup safe
   string implementation

docs/quickstart.rst

@@ -8,8 +8,8 @@ Installation
 ------------
 
 Install Pelican (and optionally Markdown if you intend to use it) on Python
-2.7.x or Python 3.5+ by running the following command in your preferred
-terminal, prefixing with ``sudo`` if permissions warrant::
+3.6+ by running the following command in your preferred terminal, prefixing
+with ``sudo`` if permissions warrant::
 
     python -m pip install "pelican[markdown]"