modify picture size (#66)

* add chengxiangwang to Committer list

* change pic to jpeg format
diff --git a/assets/images/about/chengxiangwang.jpeg b/assets/images/about/chengxiangwang.jpeg
index 85e7068..0bd23c5 100644
--- a/assets/images/about/chengxiangwang.jpeg
+++ b/assets/images/about/chengxiangwang.jpeg
Binary files differ