isEmpty() method correction.

Empty stack is at -1 index position.
Index position 0 indicates that the stack has one element in it.

Author: AlphaVS-76

src/com/mehmetpekdemir/stack/arraystack/ArrayStack.java

@@ -49,7 +49,7 @@ public Employee peek() {
 	}
 
 	public boolean isEmpty() {
-		return top == 0;
+		return top == -1;
 	}
 
 	public int size() {