Revert "remove osx"

This reverts commit 8dcae46.

Author: blueyed

.travis.yml

@@ -16,6 +16,21 @@ install:
 
 jobs:
   include:
+    # OSX tests - first (in test stage), since they are the slower ones.
+    # Coverage for:
+    # - osx
+    # - verbose=1
+    - os: osx
+      osx_image: xcode10.1
+      language: generic
+      env: TOXENV=py37-xdist PYTEST_COVERAGE=1 PYTEST_ADDOPTS=-v
+      before_install:
+        - which python3
+        - python3 -V
+        - ln -sfn "$(which python3)" /usr/local/bin/python
+        - python -V
+        - test $(python -c 'import sys; print("%d%d" % sys.version_info[0:2])') = 37
+
     # Full run of latest supported version, without xdist.
     # Coverage for:
     # - pytester's LsofFdLeakChecker