fix(bloom): optimize the calculation of k

[chenat9]

Accroding to theWIKIPEDIA, optimized the calculation of k (the number of hash functions) in bloomFilter

---

This change is 

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

chencunge seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue was marked as stale and no activity has occurred since then, therefore it will now be closed. Please, reopen if the issue is still relevant.