travis: Decrease build duration by starting OSX build early.

Looking at the recent build history the time it takes just to complete the
OSX build is already 12 minutes so make it start early, which brings down
the total build time from about 20 minutes to 14 minutes.

.travis.yml

@@ -37,6 +37,25 @@ jobs:
         - tools/codeformat.py
         - git diff --exit-code
 
+    # unix port on OSX (first in list because the build VM takes a long time to start)
+    - stage: test
+      os: osx
+      osx_image: xcode11.3
+      env:
+        - NAME="unix port build with clang on OSX"
+        - PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig
+      script:
+        - make ${MAKEOPTS} -C mpy-cross
+        - make ${MAKEOPTS} -C ports/unix submodules
+        - make ${MAKEOPTS} -C ports/unix deplibs
+        - make ${MAKEOPTS} -C ports/unix
+        # OSX has poor time resolution and the following tests do not have the correct output
+        - (cd tests && ./run-tests --exclude 'uasyncio_(basic|heaplock|lock|wait_task)')
+        # check for additional compiler errors/warnings
+        - make ${MAKEOPTS} -C ports/unix VARIANT=coverage
+      after_failure:
+        - tests/run-tests --print-failures
+
     # stm32 port
     - stage: test
       env: NAME="stm32 port build"
@@ -204,25 +223,6 @@ jobs:
       after_failure:
         - tests/run-tests --print-failures
 
-    # unix port on OSX
-    - stage: test
-      os: osx
-      osx_image: xcode11.3
-      env:
-        - NAME="unix port build with clang on OSX"
-        - PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig
-      script:
-        - make ${MAKEOPTS} -C mpy-cross
-        - make ${MAKEOPTS} -C ports/unix submodules
-        - make ${MAKEOPTS} -C ports/unix deplibs
-        - make ${MAKEOPTS} -C ports/unix
-        # OSX has poor time resolution and the following tests do not have the correct output
-        - (cd tests && ./run-tests --exclude 'uasyncio_(basic|heaplock|lock|wait_task)')
-        # check for additional compiler errors/warnings
-        - make ${MAKEOPTS} -C ports/unix VARIANT=coverage
-      after_failure:
-        - tests/run-tests --print-failures
-
     # windows port via mingw
     - stage: test
       env: NAME="windows port build via mingw"