Bump gulp-sourcemaps from 1.12.1 to 2.6.4

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>

package.json

@@ -59,7 +59,7 @@
     "gulp-rename": "^1.2.2",
     "gulp-replace": "^1.0.0",
     "gulp-sass": "^4.0.2",
-    "gulp-sourcemaps": "^1.6.0",
+    "gulp-sourcemaps": "^2.6.4",
     "gulp-util": "^3.0.7",
     "hammerjs": "^2.0.4",
     "isparta": "^4.0.0",