travis: reorder envs, remove 3.6-dev

flake8 first, 34/35/36/37 linux, 34/35/36 osx

also remove quotes around version number, not needed for 3.7.

.travis.yml

@@ -9,6 +9,10 @@ cache:
 # note: use py 3.5.2, it has lzma support. 3.5(.0) on travis.org/trusty does not.
 matrix:
     include:
+        - python: 3.4
+          os: linux
+          dist: trusty
+          env: TOXENV=flake8
         - python: 3.4
           os: linux
           dist: trusty
@@ -21,15 +25,7 @@ matrix:
           os: linux
           dist: trusty
           env: TOXENV=py36
-        - python: 3.4
-          os: linux
-          dist: trusty
-          env: TOXENV=flake8
-        - python: "3.6-dev"
-          os: linux
-          dist: trusty
-          env: TOXENV=py36
-        - python: "3.7"
+        - python: 3.7
           os: linux
           dist: xenial
           env: TOXENV=py37