Gulp Sourcemaps Versions Save

Nothing changed to the overall API.

However the following security fixes lead to the following:

• acorn which caused us to drop support for Node < 6 https://github.com/gulp-sourcemaps/gulp-sourcemaps/pull/376/files
• css bump #380

The foobar is described here https://github.com/floridoo/gulp-sourcemaps/commit/2d8c319a5c8477a6e2f27ce42009b0109faa7421

• Run sourceMappingURLPrefix function individually for every file.

• Dependency update (convert-source-map)

• uses graceful-fs for more robust file system access
• the BOM is now stripped from files loaded from the file system
• updated badge URLs in the README

• Use sourceRoot (if set) as root path to load missing sourcesContent
• Always use correct (unix style) path on Windows
• Updated dependencies
• Run automated tests on more platforms: Node 0.10, Node 0.12, io.js