Typo fix.

Change-Id: I1a82513d961a510ea76817b5b2040d180cd5b7f1

Author: wwwind

RELEASE.md

@@ -38,7 +38,7 @@ Keras clustering API:
 progress for TensorBoard.
 * Added ClusterableLayer API to support clustering of a keras custom layer.
 In addition, now clustering can be done for bias of the layer.
-* Introduced two new experimental quantization scheme for Quantization Aware Training
+* Introduced two new experimental quantization schemes for Quantization Aware Training
 for collaborative model optimization:
     - Prune Preserve QAT: pruned model can be QAT trained with preserved sparsity;
     - Cluster Preserve QAT: clustered model can be QAT trained with preserved clustering;