RestClient renamed poolsize key

RestClient does not have POOL_SIZE_KEY anymore.
From the source it is probably renamed to HTTP_POOL_SIZE.
The previous constant value was poolsize and the new constant
is http.poolsize.

Upgrading the R2, Data, Pegasus libraries along with this change.
Thanks for the comment. The key is not under our control and declared by our partners in restli team. I am not sure when they renamed. https://github.com/linkedin/rest.li/blob/master/r2/src/main/java/com/linkedin/r2/transport/http/client/HttpClientFactory.java#L88 

I appreciate your comment :) and thanks for it.