minor: Add missing word to "sending messages" doc.
minor: Add missing word to "sending messages" doc.

rht/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,rht/zulip,zulip/zulip,andersk/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip,kou/zulip,andersk/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,zulip/zulip,kou/zulip,kou/zulip,andersk/zulip,kou/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip