Use https in survery link

Signed-off-by: Harry Chen <[email protected]>

definitions.tex

@@ -51,7 +51,7 @@
 \newcommand{\ThuThesisRepo}{tuna/thuthesis}
 \newcommand{\ThuThesisLink}{https://github.com/\ThuThesisRepo}
 
-\newcommand{\surveylink}{http://wenjuan.tsinghua.edu.cn/s/yAbUNz}
+\newcommand{\surveylink}{https://wenjuan.tsinghua.edu.cn/s/yAbUNz}
 \newcommand{\thudownloadlink}{https://stu.cs.tsinghua.edu.cn/\~harry/latex-talk.pdf}
 \newcommand{\githubrepo}{tuna/thulib-latex-talk}
 \newcommand{\githublink}{https://github.com/\githubrepo}