Fix translation.
   - rename zme_recv to req_recv in chapter 1
   - fix 'SUB、PULL、REQ、REP不会有接收队列。' in chapter 2
   - fix typo '每个县城管理一个套接字' in chapter 4
   - remove duplicate text in chapter 4.
Merge pull request #3 from schemacs/master

Fix translation.