add upgrade flag to dev requirements
diff --git a/.travis.yml b/.travis.yml
index c699fbb..f7b0fed 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,7 @@
 - '3.8'
 install:
 - pip install -r requirements.txt
-- pip install -r dev_requirements.txt
+- pip install -r dev_requirements.txt --upgrade
 - pip install coveralls
 script:
 - pytest --cov