Swap 3.7 Travis build stage with 3.9 for security purposes

Signed-off-by: Victoria Miltcheva <[email protected]>

.travis.yml

@@ -17,12 +17,12 @@ deploy:
           repo: IBM/detect-secrets
 matrix:
     include:
-        - env: TOXENV=py37
-          python: 3.7.13
-          dist: xenial # Required for Python >= 3.7 (travis-ci/travis-ci#9069), the GitHub Travis build will use Python 3.7.1 by default if you provide 3.7 without a patch version and the build will fail with AttributeError: 'str' object has no attribute 'name'
         - env: TOXENV=py38
           python: 3.8
           dist: xenial # Required for Python >= 3.7 (travis-ci/travis-ci#9069)
+        - env: TOXENV=py39
+          python: 3.9
+          dist: xenial # Required for Python >= 3.7 (travis-ci/travis-ci#9069)
 before_install:
     - echo -e "machine github.com\n  login $GH_ACCESS_TOKEN" >> ~/.netrc # Login to GitHub
     - echo -e "machine github.ibm.com\n  login $GHE_ACCESS_TOKEN" >> ~/.netrc # Login to GitHub Enterprise