travis: Make 3.7 the build leader/deployer

.travis.yml

@@ -127,7 +127,7 @@ script:
 
 deploy:
   # release for main pypi
-  # 3.6 is considered the build leader and does the deploy, otherwise there is
+  # 3.7 is considered the build leader and does the deploy, otherwise there is
   # a race and all versions will try to deploy
   # OTOH if we ever need separate binary wheels then each version needs its
   # own deploy
@@ -139,5 +139,5 @@ deploy:
     on:
       branch: master
       tags: true
-      condition: $TRAVIS_PYTHON_VERSION == "3.6" && $TRAVIS_OS_NAME == "linux"
+      condition: $TRAVIS_PYTHON_VERSION == "3.7" && $TRAVIS_OS_NAME == "linux"
     skip_upload_docs: true