fix small bugs.

Author: beginor

Structural/Specification/Program.cs

@@ -13,7 +13,7 @@ public static void Main(string[] args) {
             };
 
             var smartSpecification = new ExpressionSpecification<Mobile>(mobile => mobile.Type == MobileType.Smart);
-            var appleSpecification = new ExpressionSpecification<Mobile>(mobile => mobile.Brand = MobileBrand.Apple);
+            var appleSpecification = new ExpressionSpecification<Mobile>(mobile => mobile.Brand == MobileBrand.Apple);
             // find all smart mobiles;
             var smartMobiles = mobiles.FindAll(mobile => smartSpecification.IsSatisfiedBy(mobile));
             // find all apple smart mobiles;