Update .travis.yml to use python 3.7 (#850)

endormi · JulienPalard · commit 6f489ae80bb0 · 2019-08-13T10:40:18.000+02:00
because the master branch is 3.7 so it's only logical to have py 3.7 as well
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,6 @@
 language: python
 dist: xenial
-python: 3.6
+python: 3.7
 before_install:
   - sudo apt-get update
   - sudo apt-get install -y hunspell hunspell-fr-comprehensive
