Tuning of a Null Move Parameter

STC:
LLR: 2.99 (-2.94,2.94) <-0.50,2.50>
Total: 78744 W: 19956 L: 19664 D: 39124
Ptnml(0-2): 259, 9005, 20573, 9255, 280
https://tests.stockfishchess.org/tests/view/6172017a38cb9784038af947

LTC:
LLR: 2.95 (-2.94,2.94) <0.50,3.50>
Total: 68528 W: 17309 L: 16964 D: 34255
Ptnml(0-2): 41, 7194, 19455, 7527, 47
https://tests.stockfishchess.org/tests/view/6172994d38cb9784038af983

closes #3756

bench: 6689428

src/search.cpp

@@ -825,7 +825,7 @@ namespace {
         && (ss-1)->statScore < 23767
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 20 * depth - improvement / 15 + 177
+        &&  ss->staticEval >= beta - 20 * depth - improvement / 15 + 204
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))