Update SendMessageProcessor.java

[shuhan-happy]

change param name (startTimstamp to startTimestamp)

What is the purpose of the change

change wrong param name

Brief changelog

startTimstamp to startTimestamp

Verifying this change

XXXX

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[coveralls]

Coverage increased (+0.05%) to 43.172% when pulling 862730c on fuchun:master into d4d02b5 on apache:master.

[liuruiyiyang]

Please merge into develop branch.

[RongtongJin]

I think the code is OK, but please merge into the develop branch and submit the corresponding issue. I'll close this PR first.