Change order of TravisCI build matrix

The most expensive builds are now scheduled immediately after the lint
builds. The coverage-test builds, pypy, and pypy3 builds take almost twice
as long as remaining builds.

By placing them first in the build matrix, parallel build scheduling may be
improved such that the total time for all builds decreases.

Signed-off-by: Peter Grayson <[email protected]>

Author: jpgrayson

.travis.yml

@@ -15,11 +15,13 @@ matrix:
     - python: '3.7'
       env: MAKE_TARGET=lint
       dist: xenial
-    - python: '2.6'
-      dist: trusty
-      env: MAKE_TARGET=test
     - python: '2.7'
       env: MAKE_TARGET=coverage-test
+    - python: '3.7'
+      env: MAKE_TARGET=coverage-test
+      dist: xenial
+    - python: 'pypy3'
+      env: MAKE_TARGET=test
     - python: 'pypy'
       env: MAKE_TARGET=test
     - python: '3.3'
@@ -31,17 +33,15 @@ matrix:
       env: MAKE_TARGET=test
     - python: '3.6'
       env: MAKE_TARGET=test
-    - python: '3.7'
-      env: MAKE_TARGET=coverage-test
-      dist: xenial
-    - python: 'pypy3'
-      env: MAKE_TARGET=test
     - python: '3.8-dev'
       env: MAKE_TARGET=test
       dist: xenial
     - python: 'nightly'
       dist: xenial
       env: MAKE_TARGET=test
+    - python: '2.6'
+      dist: trusty
+      env: MAKE_TARGET=test
   allow_failures:
     - python: '3.8-dev'
     - python: 'nightly'