fix: expressions, update isBinary behavior according to the spec

I will update test cases in the next commit

See: https://github.com/vrm-c/vrm-specification/blob/master/specification/VRMC_vrm-1.0/expressions.md#expression-specification

The suggestion: #1489

Co-authored-by: ke456-png <108649297+ke456-png@users.noreply.github.com>

packages/three-vrm-core/src/expressions/VRMExpression.ts

@@ -92,7 +92,7 @@ export class VRMExpression extends THREE.Object3D {
    */
   public get outputWeight(): number {
     if (this.isBinary) {
-      return this.weight >= 0.5 ? 1.0 : 0.0;
+      return this.weight > 0.5 ? 1.0 : 0.0;
     }
 
     return this.weight;