Don't try to uninstall packages on Travis

scripts/travis

@@ -41,7 +41,7 @@ fi
 echo "$TRAVIS_BRANCH" | grep -qvE "^[0-9.]+$" && exit 0; :;
 
 # Install dependencies for release build
-pip install --ignore-installed wheel twine
+pip install --ignore-installed twine
 
 # Build and install theme and Docker image
 python setup.py build sdist bdist_wheel --universal