Updated test builds to support node10 and 12.

The filepath property overrides filename and may contain a relative path. This is typically used when uploading multiple files from a directory.

Thanks to @sebdeckers

• toString will output '[object FormData]'
  Thanks to @m59peacemaker

Checks for self object, if not found, falls back to window object.

& updated dependencies

• To improve node-fetch integration

• Dropped support for node@0.10
• Cleaned up code and tools.

• Avoid undefined variable reference in older browsers #176
• Refreshed dependencies
• Housecleaning