A couple more script tweaks for clarity

- Because the substitition string after the hyphen is empty,
  "${VIRTUAL_ENV:-}" and "${VIRTUAL_ENV-}" have the same effect.
  However, the latter, which this changes it to, expresses the
  correct idea that the special case being handled is when the
  variable is unset: in this case, we expand an empty field rather
  than triggering an error due to set -u. When the variable is set
  but empty, it already expands to the substitution value, and
  including that in the special case with ":" is thus misleading.

- Continuing in the vein of d18d90a (and 1e0b3f9), this removes
  another explicit newline by adding another echo command to print
  the leading blank line before the table.

build-release.sh

@@ -14,7 +14,7 @@ function suggest_venv() {
     printf "HELP: To avoid this error, use a virtual-env with '%s' instead.\n" "$venv_cmd"
 }
 
-if test -n "${VIRTUAL_ENV:-}"; then
+if test -n "${VIRTUAL_ENV-}"; then
     deps=(build twine)  # Install twine along with build, as we need it later.
     echo "Virtual environment detected. Adding packages: ${deps[*]}"
     pip install --quiet --upgrade "${deps[@]}"

check-version.sh

@@ -41,7 +41,8 @@ head_sha="$(git rev-parse HEAD)"
 latest_tag_sha="$(git rev-parse "${latest_tag}^{commit}")"
 
 # Display a table of all the current version, tag, and HEAD commit information.
-echo $'\nThe VERSION must be the same in all locations, and so must the HEAD and tag SHA'
+echo
+echo 'The VERSION must be the same in all locations, and so must the HEAD and tag SHA'
 printf '%-14s = %s\n' 'VERSION file'   "$version_version" \
                       'changes.rst'    "$changes_version" \
                       'Latest tag'     "$latest_tag" \