[Azure Pipelines] Update `pod lib lint` to Xcode 10.2

azure-pipelines.yml

@@ -70,9 +70,9 @@ jobs:
 
 - job: pod_lib_lint
   pool:
-    vmImage: 'macOS-10.13'
+    vmImage: 'macOS-10.14'
   variables:
-    DEVELOPER_DIR: '/Applications/Xcode_9.4.1.app'
+    DEVELOPER_DIR: '/Applications/Xcode_10.2.app'
   steps:
     - script: pod lib lint
       displayName: pod lib lint