build a binary wheel on Linux as well

.travis.yml

@@ -12,3 +12,5 @@ script:
 install:
  - pip install -r requirements.txt
  - python setup.py install
+after_success:
+  - bash build.sh

build.sh

+#!/bin/bash
+
+set -x
+set -e
+
+if [ $TRAVIS_BRANCH == "master" ]; then
+    pip install wheel twine
+    python setup.py bdist bdist_wheel
+    twine upload -u $PYPI_USER -p $PYPI_PWD dist/*
+fi