Fix unused variable warning.

Looking at the code, it looks like it caught an actual bug.

```
protocol-http-0.47.1/lib/protocol/http/body/stream.rb:263: warning: assigned but unused variable - buffer
```

Author: byroot

lib/protocol/http/body/stream.rb

@@ -263,7 +263,7 @@ def gets(separator = NEWLINE, limit = nil, chomp: false)
 								buffer = @buffer
 								@buffer = nil
 
-								return @buffer
+								return buffer
 							end
 						end