create_source_tarball.sh: Use UTC timezone when determining the prerelease date

Author: cameel

scripts/create_source_tarball.sh

@@ -15,7 +15,7 @@ if [[ -e prerelease.txt && ! -s prerelease.txt ]]; then
 elif [[ -e prerelease.txt ]]; then
     version_string="${version}-$(cat prerelease.txt)-${commit_hash}"
 else
-    commit_date=$(git show --format=%ci HEAD | head -n 1 | cut - -b1-10 | sed -e 's/-0?/./' | sed -e 's/-0?/./')
+    commit_date=$(TZ=UTC git show --quiet --date="format-local:%Y.%-m.%-d" --format="%cd")
     version_string="${version}-nightly-${commit_date}-${commit_hash}"
 fi