[Site] Update graduate TAs roles (#94)

Co-authored-by: Soo Yuen Jien <yuenjiensoo@gmail.com>

Author: didymusne

website/components/students.json

@@ -27,14 +27,14 @@
         "name": "Ruppa Nagarajan Sivayoga Subramanian",
         "id": "ruppa-nagarajan-sivayoga-subramanian",
         "image": "/img/staff/ruppa-nagarajan-sivayoga-subramanian.jpg",
-        "role": "Tutor",
+        "role": "Teaching Assistant",
         "url": "https://sivarn.com"
       },
       {
         "name": "Zhang Ziqing",
         "id": "zhang-ziqing",
         "image": "/img/staff/zhang-ziqing.jpg",
-        "role": "Tutor",
+        "role": "Teaching Assistant",
         "url": "https://www.linkedin.com/in/ziqingzhang26/"
       },
       {