Mail: fixed a comment.

src/mail/ngx_mail.c

diff --git a/src/mail/ngx_mail.c b/src/mail/ngx_mail.c
index 5a7cb6b..bf1b858 100644
--- a/src/mail/ngx_mail.c
+++ b/src/mail/ngx_mail.c
@@ -98,7 +98,7 @@
 
     *(ngx_mail_conf_ctx_t **) conf = ctx;
 
-    /* count the number of the http modules and set up their indices */
+    /* count the number of the mail modules and set up their indices */
 
     ngx_mail_max_module = 0;
     for (m = 0; ngx_modules[m]; m++) {