No support for JavaScript Proxy?

Build Environment
1

I have code that uses JavaScriptCore to wrap some objects passed to JS context with a Proxy object. It works fine locally (Sierra 10.12.4), but when running tests on CI they fail with “ReferenceError: Can’t find variable: Proxy”

Here is the config:

machine:
  xcode:
    version: 8.2
  environment:
    XCODE_WORKSPACE: Sourcery.xcworkspace
    XCODE_SCHEME: Sourcery
  post:
      - ln -s /Applications/Xcode-8.2.app /Applications/Xcode.app

test:
  override:
      - set -o pipefail
      - xcodebuild -workspace "$XCODE_WORKSPACE" -scheme "$XCODE_SCHEME" ONLY_ACTIVE_ARCH=NO CODE_SIGN_IDENTITY="" CODE_SIGNING_REQUIRED=NO build | xcpretty
      - xcodebuild -workspace "$XCODE_WORKSPACE" -scheme "$XCODE_SCHEME" ONLY_ACTIVE_ARCH=NO CODE_SIGN_IDENTITY="" CODE_SIGNING_REQUIRED=NO test | tee $CIRCLE_ARTIFACTS/xcode_raw.log | xcpretty --color --report junit --output $CIRCLE_TEST_REPORTS/xcode/results.xml
      - swift build
  post:
      - bash <(curl -s https://codecov.io/bash)
      - bundle exec danger
2

Solved by updating image to Xcode 8.3