Update the check job on Travis to avoid losing it

Author: altendky

.travis.yml

@@ -5,8 +5,6 @@ env:
   global:
     - LD_PRELOAD=/lib/x86_64-linux-gnu/libSegFault.so
     - SEGFAULT_SIGNALS=all
-  matrix:
-    - TOXENV=check
 matrix:
   include:
     - python: '3.6'
@@ -22,6 +20,11 @@ matrix:
       sudo: required
       env:
         - TOXENV=doc
+    - python: '3.7'
+      dist: xenial
+      sudo: required
+      env:
+        - TOXENV=check
 before_install:
   - python --version
   - uname -a