Fix a typo in 4cdcf4e

Signed-off-by: Shengqi Chen <harry-chen@outlook.com>

thuthesis.dtx

@@ -4586,7 +4586,7 @@
 \newcommand\thu@set@student@id{%
   \ifthu@thesis@type@proposal\else
     \ifx\thu@student@id\@empty\else
-      \thu@warning{`studen-id' in "\protect\thusetup" would be ignored when `thesis-type' is not proposal.}%
+      \thu@warning{`student-id' in "\protect\thusetup" would be ignored when `thesis-type' is not proposal.}%
     \fi
   \fi
 }