travis: pip install as user

.travis.yml

@@ -8,7 +8,7 @@ env:
         - PIP_DOWNLOAD_CACHE="${HOME}/.pip-cache"
 before_script:
     - ./scripts/bootstrap-depends.sh ${HOME}/fakeroot
-    - pip install -r tests/pydnstest/requirements.txt
+    - pip install --user travis -r tests/pydnstest/requirements.txt
 script:
     - autoreconf -i
     - ./configure --enable-integration-tests