Allow empty string as destination path
Allow empty string as destination path

Closes #150

gulp-sourcemaps/gulp-sourcemaps,realtymaps/gulp-sourcemaps,floridoo/gulp-sourcemaps,floridoo/gulp-sourcemaps,realtymaps/gulp-sourcemaps,gulp-sourcemaps/gulp-sourcemaps,realtymaps/gulp-sourcemaps,floridoo/gulp-sourcemaps,gulp-sourcemaps/gulp-sourcemaps