macos: readd coverage

Author: blueyed

.travis.yml

@@ -29,7 +29,7 @@ jobs:
       # Coverage for:
       # - py2 with symlink in test_cmdline_python_package_symlink.
       # - _pytest.unittest._handle_skip (via pexpect).
-      env: TOXENV=py27-pexpect-xdist
+      env: TOXENV=py27-pexpect-xdist PYTEST_COVERAGE=1
       before_install:
         - python -V
         - test $(python -c 'import sys; print("%d%d" % sys.version_info[0:2])') = 27