Deploy to PyPI using twine

Deploying via Travis' built-in method (using the `pypi` provider) wasn't
doing anything (nor reporting any errors).
Deploying using the `script` provider simply failed with no output
(though that *is* experimental), so use `after_success` instead.

Author: Hugo Osvaldo Barrera

.travis.yml

@@ -57,19 +57,12 @@ script:
 after_script:
   - codecov
 
-before_deploy:
-  - pip install wheel
+after_success:
+  - pip install wheel twine
   - python setup.py sdist bdist_wheel
+  - test -n $TRAVIS_TAG && twine upload -u $PYPI_USERNAME -p $PYPI_PASSWORD dist/*
 
 deploy:
-  - provider: pypi
-    user: hobarrera
-    password:
-      secure: LXSgJZMZICS0Xv5qyR/IRgki1Wy23lurmdepsOsjzBM2fv7rgKPlU/MASVCUCmLi9vYYqZu+7ViHeT6uhJXLdwE0NisVYqTg6L4aD1kqDmbjkWFhLKA7DAz1QTAYxrk6TQYmDb+ZbNFZlF21g29nqvqtLwdC4dFnDjXGnupCoeU=
-    on:
-      tags: true
-    distributions: "sdist bdist_wheel"
-    server: https://upload.pypi.org/legacy/
   - provider: releases
     api_key:
       secure: g60yeYa+BX7XCe7L4mpV5NiaCPkuJzxk+PP3rL/durPF/CudWW2xUuTCLf30WwfrYBg3bJCQKNnzOpL8+d4Maly3UqquDFjK58Z/JBFw6erzg/RAxAnfJzFbWy2mgqKTpBHaDdRnhVtqp23Ov1I/+Jb51DIhij6ILNgGxW1OP8Y=

CHANGELOG.rst

@@ -4,6 +4,12 @@ Changelog
 This file contains a brief summary of new features and dependency changes or
 releases, in reverse chronological order.
 
+v3.2.4
+------
+
+* Deploy new versions to PyPI using ``twine``. Travis doesn't seem to be
+  working.
+
 v3.2.3
 ------