Fix swig version at 3 and upgrade macOS image version (#2120)

* update

* upgrade macos and remove swig

* update macos version

* clean up

azure-pipelines.yml

@@ -77,7 +77,7 @@ jobs:
 
 - job: 'basic_test_pr_macOS'
   pool:
-    vmImage: 'macOS 10.13'
+    vmImage: 'macOS-10.15'
   strategy:
     matrix:
       Python36:
@@ -94,8 +94,8 @@ jobs:
       python3 -m pip install torch==1.2.0 --user
       python3 -m pip install torchvision==0.4.0 --user
       python3 -m pip install tensorflow==1.13.1 --user
-      ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" < /dev/null 2> /dev/null
       brew install swig@3
+      rm /usr/local/bin/swig
       ln -s /usr/local/opt/swig\@3/bin/swig /usr/local/bin/swig
       nnictl package install --name=SMAC
     displayName: 'Install dependencies'