Fix clobbering of .env file
This fixes an issue that was introduced in https://gitlab.builder.ai/public-tools/deploy-templates/-/merge_requests/455/diffs. Some repo's have a pre-populated .env file with no new lines at the end, this causes appends to clobber the .env file, here is an example:
SKIP_PREFLIGHT_CHECK=trueREACT_APP_BASE_URL=https://store.builder.ai/restaurant/restaurantwebsiteapp398946
This change adds a new line before appending, so outputs will now be either of the two below depending on if a newline was already present or now:
SKIP_PREFLIGHT_CHECK=true
REACT_APP_BASE_URL="https://store.builder.ai/restaurant/degreesafricanrestaurantandbar401394"
or
SKIP_PREFLIGHT_CHECK=true
REACT_APP_BASE_URL="https://store.builder.ai/restaurant/degreesafricanrestaurantandbar401394"