Keyword 61行未对tfidfvalue相等的情况做判断

[Wang-Kowah]

@Override
public int compareTo(Keyword o)
{
    return this.tfidfvalue-o.tfidfvalue>0?-1:1;
}

JDK.1.8下，当两个关键词的tfidfvalue相等时会抛出异常IllegalArgumentException: Comparison method violates its general contract! 按照以下方式改写即可：

@Override
public int compareTo(Keyword o)
{
    return this.tfidfvalue - o.tfidfvalue > 0 ? -1 : (this.tfidfvalue == o.tfidfvalue ? 0 : 1);
}