Drop Python 3.2 support

See also pip>=8.0.0 has the backwards incompatible change of having dropped Python 3.2 support:
https://pip.pypa.io/en/stable/news/#release-notes

.travis.yml

@@ -28,7 +28,6 @@ env:
   - TOX_ENV=flake8
   - TOX_ENV=py26
   - TOX_ENV=py27
-  - TOX_ENV=py32
   - TOX_ENV=py33
   - TOX_ENV=py34
   - TOX_ENV=py35

README.rst

@@ -22,7 +22,6 @@ makes sure premailer works in:
 
 -  Python 2.6
 -  Python 2.7
--  Python 3.2
 -  Python 3.3
 -  Python 3.4
 -  Python 3.5

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = flake8, py26, py27, py32, py33, py34, py35, pypy
+envlist = flake8, py26, py27, py33, py34, py35, pypy
 
 [testenv]
 passenv = *
@@ -25,21 +25,6 @@ deps =
 deps = flake8
 commands = flake8 premailer
 
-[testenv:py32]
-# Python 3.2 does not support coverage 4.x
-commands = nosetests --with-coverage --cover-package=premailer
-install_command =
-  pip install {opts} {packages}
-
-deps =
-    setuptools
-    nose
-    mock
-    cssselect
-    cssutils
-    lxml
-    coverage==3.7.1
-
 [testenv:py26]
 # Python 2.6 is missing both the ordereddict and argparse modules
 # from the standard library.