Travis CI: The real Python 3.7 in a separate parallel run

.travis.yml

@@ -58,10 +58,15 @@ matrix:
         env:
           - CMAKE_OPTS="-DBUILD_FEM_NETGEN=ON"
           - PYTHON_MAJOR_VERSION=3
-        before_script:
-          - python3 -m pip install flake8
-          # fail the build if there are Python syntax errors
-          - flake8 . --count --select=E901,E999,F822,F823 --show-source --statistics
+
+      - language: python
+        python: 3.7
+        dist: xenial
+        before_install: true
+        install: python3 -m pip install flake8
+        # fail the build if there are Python syntax errors
+        script: flake8 . --count --select=E901,E999,F822,F823 --show-source --statistics
+
 
 # This is commented out to stop permanently failing osx builds. Please check this thread for the details:
 # https://forum.freecadweb.org/viewtopic.php?f=10&t=32272