Allow failure for macOS job on AppVeyor

appveyor.yml

@@ -7,6 +7,10 @@ environment:
     - APPVEYOR_BUILD_WORKER_IMAGE: macos-mojave
       APPVEYOR_JOB_NAME: "python37-x64-macos-mojave"
 
+matrix:
+  allow_failures:
+    - APPVEYOR_BUILD_WORKER_IMAGE: macos-mojave
+
 stack: python 3.7
 
 build: off
@@ -15,11 +19,11 @@ init:
 - cmd: set PATH=C:\Python37;C:\Python37\Scripts;%PATH%
 - ps: |
       $BRANCH = if ($env:APPVEYOR_PULL_REQUEST_HEAD_REPO_BRANCH) { $env:APPVEYOR_PULL_REQUEST_HEAD_REPO_BRANCH } else { $env:APPVEYOR_REPO_BRANCH }
-      if ($BRANCH -eq 'master' -or $BRANCH.ToLower().StartsWith('appveyor-')) {
+      if (-not ($BRANCH -eq 'master' -or $BRANCH.ToLower().StartsWith('appveyor-'))) {
         $env:PYTEST_ADDOPTS='-k "unit_test or _basic" --suppress-no-test-exit-code'
       }
 
-install: python -m pip install --retries 3 -r requirements-dev.txt pytest-custom-exit-code
+install: python -m pip install -r requirements-dev.txt pytest-custom-exit-code
 
 # the '-u' flag is required so the output is in the correct order.
 # See https://github.com/joerick/cibuildwheel/pull/24 for more info.