build: fix appveyor cache failures (GoogleChrome#10281)

Author: jayaddison

.appveyor.yml

@@ -41,6 +41,12 @@ test_script:
   # FIXME: Exclude Appveyor from running `lantern` smoketest until we fix the flake.
   - yarn smoke -j=1 --retries=2 a11y errors oopif pwa pwa2 pwa3 dbw redirects seo offline byte perf metrics
 
+on_success:
+  # Remove module resolution symlinks; this avoids 'Unable to save cache'
+  # errors when appveyor runs 7z.exe to save the build cache
+  - yarn unlink lighthouse
+  - yarn unlink
+
 cache:
   #- chrome-win32 -> appveyor.yml,package.json
   - node_modules -> appveyor.yml,package.json,yarn.lock