Switch back to 10.14 again

10.15 fails in the same way with or without conda, we've tried 10.14
without conda but not with it. This commit switches back to 10.14 now
that we've switched to using conda to see if the tests pass.

azure-pipelines.yml

@@ -62,7 +62,7 @@ stages:
             TWINE_PASSWORD: $(TWINE_PASSWORD)
     - job: 'macos'
       condition: startsWith(variables['Build.SourceBranch'], 'refs/tags')
-      pool: {vmImage: 'macOS-10.15'}
+      pool: {vmImage: 'macOS-10.14'}
       variables:
         python.version: '3.7'
         CIBW_BEFORE_BUILD: pip install -U Cython
@@ -223,7 +223,7 @@ stages:
             pathtoPublish: 'docs/_build/html'
             artifactName: 'html_docs'
     - job: 'MacOS_Catalina_Tests'
-      pool: {vmImage: 'macOS-10.15'}
+      pool: {vmImage: 'macOS-10.14'}
       condition: not(startsWith(variables['Build.SourceBranch'], 'refs/tags'))
       strategy:
         matrix:
@@ -398,7 +398,7 @@ stages:
             testResultsFiles: '**/test-*.xml'
             testRunTitle: 'Test results for Linux Python $(python.version)'
     - job: 'MacOS_Catalina_Tests'
-      pool: {vmImage: 'macOS-10.15'}
+      pool: {vmImage: 'macOS-10.14'}
       condition: not(startsWith(variables['Build.SourceBranch'], 'refs/tags'))
       strategy:
         matrix: