Move slow MacOS builds higher up in the travis build matrix to make them start...

Move slow MacOS builds higher up in the travis build matrix to make them start earlier and reduce the overall turn-over time.

.travis.yml

@@ -39,17 +39,7 @@ env:
 
 matrix:
   include:
-# Disabled: coverage analysis takes excessively long, several times longer than without.
-#    - python: 3.7
-#      env: COVERAGE=1
-    - python: 3.7
-      env: TEST_CODE_STYLE=1
-    - python: 3.8
-      env: LIMITED_API=--limited-api EXCLUDE=--no-file
-    - python: 3.7
-      env: LIMITED_API=--limited-api EXCLUDE=--no-file
-    - python: 3.6
-      env: LIMITED_API=--limited-api EXCLUDE=--no-file
+    # slowest first
     - os: osx
       osx_image: xcode6.4
       env: PY=2
@@ -64,6 +54,17 @@ matrix:
       language: c
       compiler: clang
       cache: false
+# Disabled: coverage analysis takes excessively long, several times longer than without.
+#    - python: 3.7
+#      env: COVERAGE=1
+    - python: 3.7
+      env: TEST_CODE_STYLE=1
+    - python: 3.8
+      env: LIMITED_API=--limited-api EXCLUDE=--no-file
+    - python: 3.7
+      env: LIMITED_API=--limited-api EXCLUDE=--no-file
+    - python: 3.6
+      env: LIMITED_API=--limited-api EXCLUDE=--no-file
     - env: STACKLESS=true BACKEND=c PY=2
       python: 2.7
     - env: STACKLESS=true BACKEND=c PY=3