Enable the spatial_segmentation experiment by default

It has been provisionally adopted for over a month now.

Change-Id: I717188c5b6ffa449440f253b1dede97c70fff510
diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 95437c3..7b9b0bc 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -175,7 +175,7 @@
 set(CONFIG_SEGMENT_PRED_LAST 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SHORT_FILTER 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SIMPLIFY_TX_MODE 1 CACHE NUMBER "AV1 experiment flag.")
-set(CONFIG_SPATIAL_SEGMENTATION 0 CACHE NUMBER "AV1 experiment flag.")
+set(CONFIG_SPATIAL_SEGMENTATION 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_STRIPED_LOOP_RESTORATION 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_TEMPMV_SIGNALING 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_TILE_INFO_FIRST 0 CACHE NUMBER "AV1 experiment flag.")