Allow Zotero.Server requests with `Host: localhost`
Allow Zotero.Server requests with `Host: localhost`

Previously only Host: 127.0.0.1 was allowed. (The check prevents a DNS
rebinding attack.)

This allows requests to translation-server using localhost
(zotero/translation-server#48).

Fixes #125

gracile-fr/zotero,gracile-fr/zotero,gracile-fr/zotero