What character do I use for the newline on Vim search and replace commands?

I'm trying to make this:

```
1, 
2, 
3, 
4, 
5 

```

to this: `1, 2, 3, 4 ,5`

So i thought of writing something like: `:%s/$/\b/g`

But it didn't work even if I set: `:set magic`.
How can I achieve that?