run coverage with go module

azure-pipelines.yml

@@ -31,23 +31,16 @@ jobs:
     vmImage: 'Ubuntu 16.04'
 
   variables:
-    GOPATH: '$(system.defaultWorkingDirectory)'
     CODECOV_TOKEN: '$(coverage.token)'
 
   steps:
-  - checkout: none
+  - checkout: self
   - task: GoTool@0
     inputs:
       version: '1.11.5'
   - script: |
-      go version
-      go get -v -t -d v2ray.com/core/...
-    workingDirectory: '$(system.defaultWorkingDirectory)'
-    displayName: 'Fetch sources'
-  - script: |
-      cd ./src/v2ray.com/core
       bash ./testing/coverage/coverall
-    workingDirectory: '$(system.defaultWorkingDirectory)'
+    workingDirectory: '$(Build.SourcesDirectory)'
     displayName: 'Coverage'
 
 - job: make_release