Tweak futility pruning constants

Based on recent improvement of futility pruning by @locutus2 : we lower
the futility margin to apply it for more nodes but as a compensation
we also lower the history threshold to apply it to less nodes. Further
work in tweaking constants can always be done - numbers are guessed
"by hand" and are not results of some tuning, maybe there is some more
Elo to squeeze from this part of code.

Passed STC
LLR: 2.98 (-2.94,2.94) {-1.00,3.00}
Total: 15300 W: 3081 L: 2936 D: 9283
Ptnml(0-2): 260, 1816, 3382, 1900, 290
http://tests.stockfishchess.org/tests/view/5e18da3b27dab692fcf9a158

Passed LTC
LLR: 2.94 (-2.94,2.94) {0.00,2.00}
Total: 108670 W: 14509 L: 14070 D: 80091
Ptnml(0-2): 813, 10259, 31736, 10665, 831
http://tests.stockfishchess.org/tests/view/5e18fc9627dab692fcf9a180

Bench: 4643972

AUTHORS

@@ -153,7 +153,7 @@ Uri Blass (uriblass)
 Vince Negri (cuddlestmonkey)
 
 
-# Additionally, we acknowledge the authors and maintainer of fishtest,
+# Additionally, we acknowledge the authors and maintainers of fishtest,
 # an amazing and essential framework for the development of Stockfish!
 #
 # https://github.com/glinscott/fishtest/blob/master/AUTHORS

src/search.cpp

@@ -1016,11 +1016,11 @@ moves_loop: // When in check, search starts from here
               // Futility pruning: parent node (~5 Elo)
               if (   lmrDepth < 6
                   && !inCheck
-                  && ss->staticEval + 255 + 182 * lmrDepth <= alpha
+                  && ss->staticEval + 235 + 172 * lmrDepth <= alpha
                   &&  thisThread->mainHistory[us][from_to(move)]
                     + (*contHist[0])[movedPiece][to_sq(move)]
                     + (*contHist[1])[movedPiece][to_sq(move)]
-                    + (*contHist[3])[movedPiece][to_sq(move)] < 30000)
+                    + (*contHist[3])[movedPiece][to_sq(move)] < 25000)
                   continue;
 
               // Prune moves with negative SEE (~20 Elo)