Changes travis CI test platforms.
Changes travis CI test platforms.

Changes:
- Removes chrome at windows XP test
- Changes firefox version from 52 to 55
- Changes firefox platform to Windows 10
- Adds google chrome test for Windows 7 and 8 platforms.

bridgedotnet/Bridge.Newtonsoft.Json,bridgedotnet/Bridge.Newtonsoft.Json,bridgedotnet/Bridge.Newtonsoft.Json