upload only once

build.sh

@@ -7,6 +7,9 @@ python compile_definitions.py
 python setup.py bdist bdist_wheel
 
 if [ $TRAVIS_BRANCH == "master" ]; then
-    pip install wheel twine
-    twine upload -u $PYPI_USER -p $PYPI_PWD dist/*
+
+    if [ $TRAVIS_PYTHON_VERSION == "2.7" ]; then
+        pip install wheel twine
+        twine upload -u $PYPI_USER -p $PYPI_PWD dist/*
+    fi
 fi