Fix follow parameter documentation for streaming
Fix follow parameter documentation for streaming

Although current `follow' parameter documentation is okay to use,
ideal type preferred for this context is `IEnumerable<long>' rather than
`IEnumerable<string>' (since Twitter accepts user IDs rather than screen
names and we use `long' as user IDs).

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