Reverted Markdown error.

format.c

@@ -94,7 +94,6 @@ static xs_str *format_line(const char *line, xs_list **attach)
             "`[^`]+`"                           "|"
             "~~[^~]+~~"                         "|"
             "\\*\\*?\\*?[^\\*]+\\*?\\*?\\*"     "|"
-            ":.+:"                              "|" //emotes
             "__[^_]+__"                         "|" //anzu
             "!\\[[^]]+\\]\\([^\\)]+\\)"         "|"
             "\\[[^]]+\\]\\([^\\)]+\\)"          "|"