remove group write bit to end up with the same we would with umask 022

This should solve the permission issue inside the container image.

.travis.yml

@@ -17,6 +17,7 @@ install:
   - sudo apt-get --yes --no-install-recommends install qemu-user-static
 before_script:
   - sudo ./prepare-qemu
+  - chmod -R g-w ./
 script:
   - ./build
 after_success: