Bumps [gulp-sourcemaps](https://github.com/gulp-sourcemaps/gulp-sourcemaps) from 1.12.1 to 2.6.4.
- [Release notes](https://github.com/gulp-sourcemaps/gulp-sourcemaps/releases)
- [Commits](https://github.com/gulp-sourcemaps/gulp-sourcemaps/compare/v1.12.1...v2.6.4)
Signed-off-by: dependabot[bot] <support@dependabot.com>