Run py38-xdist as part of the build instead of cron

Author: nicoddemus

.travis.yml

@@ -55,10 +55,8 @@ jobs:
     - env: TOXENV=py37-pluggymaster-xdist
     - env: TOXENV=py37-freeze
 
-    # Jobs only run via Travis cron jobs (currently daily).
     - env: TOXENV=py38-xdist
       python: '3.8-dev'
-      if: type = cron
 
     - stage: baseline
       env: TOXENV=py36-xdist