add missing include of <algorithm>

Summary: `folly/stats/StreamingStats.h` uses `std::min` and `std::max` so must `#include <algorithm>`.

Reviewed By: Orvid

Differential Revision: D27986054

fbshipit-source-id: 1c1160101e1ebb4e0b1a16d3d97fd2931db9eeb0

folly/stats/StreamingStats.h

@@ -16,6 +16,7 @@
 
 #pragma once
 
+#include <algorithm>
 #include <cmath>
 #include <functional>
 #include <limits>