Fix #6: explicitly set write permission to the ${PROJECT_DIR}
This commit fixes #6 (closed) by adding a chmod command in front of the rm -r command that removes the complete ${PROJECT_DIR} before
deploying the new project. This became necessary after the upgrade of
the R renv package to v0.17.0, which made renv's sandbox directory
non-writable.
See also shiny/shadoc#133.