IPアドレスの一覧表の形式を修正

        <thead>
          <tr>
            <th>IPアドレス</th>
            <th>アクセス回数</th>
            <th>初回のアクセス日時</th>
            <th>最新のアクセス日時</th>
          </tr>
        </thead>
        <tbody v-for="item in ipHistory" :key="item.ipAddress">
          <tr>
            <td>{{ item.ipAddress }}</td>
            <td>{{ item.accessCount }}</td>
            <td>{{ item.firstAccessDate }}</td>
            <td>{{ item.lastAccessDate }}</td>
          </tr>
        </tbody>

    addIpHistory(id, ipAddress, accessDate) {
      const index = this.ipHistory.findIndex(
        address => address.ipAddress === ipAddress
      );
      if (index == -1) {
        this.ipHistory.unshift({
          id: id,
          ipAddress: ipAddress,
          accessCount: 1,
          firstAccessDate: accessDate,
          lastAccessDate: accessDate
        });
      } else {
        if (this.ipHistory[index].firstAccessDate > accessDate) {
          this.ipHistory[index].firstAccessDate = accessDate;
        }
        if (this.ipHistory[index].lastAccessDate < accessDate) {
          this.ipHistory[index].lastAccessDate = accessDate;
        }
        this.ipHistory[index].accessCount++;
      }
    },