Downgrade the Newtonsoft.Json.dll to the release 4.5
Downgrade the Newtonsoft.Json.dll to the release 4.5

This commit is for the mono 2.10 compatibility.

azyobuzin/LibAzyotter,haripo/CoreTweet,cannorin/CoreTweet,VSALM/CoreTweet,chitoku-k/CoreTweet,VSALM/CoreTweet