On Linux, the test runner for VSCode extensions uses invalid permissions (755 decimal => -wxrw--wt) for VSCode-linux-x64/code.
Although this does not prevent test because the owner has 'x' permission (accidentally), this causes failure of caching by CI.

For example:

• https://travis-ci.org/kimushu/rubic-vscode/jobs/302262680
  • Test succeeded at L1466
  • code has invalid permission at L1478
  • Making cache failed at L1514

Improved by this patch:

• https://travis-ci.org/kimushu/rubic-vscode/jobs/302270218
  • Patched at L1263
  • Test succeeded at L1466
  • code has valid permission at L1478
  • Making cache succeeded at L1513