use cache for linting as well

.ci/azure-pipelines.yml

@@ -84,8 +84,16 @@ jobs:
       inputs:
         versionSpec: '10.x'
 
-    - script: 'yarn install'
+    - task: Cache@2
+      displayName: 'Check Cache'
+      inputs:
+        key: 'yarn | yarn.lock'
+        path: 'node_modules'
+        cacheHitVar: CACHE_RESTORED
+
+    - script: 'yarn install --pure-lockfile'
       displayName: 'Install Dependencies'
+      condition: ne(variables.CACHE_RESTORED, 'true')
 
     - script: 'yarn run lint'
       displayName: 'Run ESLint'