update exercises

data/2.算法中阶/4.leetcode-栈与队列/6.155-最小栈/solution.md

@@ -29,10 +29,10 @@ MinStack minStack = new MinStack();
 minStack.push(-2);
 minStack.push(0);
 minStack.push(-3);
-minStack.getMin();   --> 返回 -3.
+minStack.getMin();   --> 返回 -3.
 minStack.pop();
-minStack.top();      --> 返回 0.
-minStack.getMin();   --> 返回 -2.
+minStack.top();      --> 返回 0.
+minStack.getMin();   --> 返回 -2.
 ```
 
 <p><strong>提示：</strong></p>