Update _config.yml

Author: nemkin

_config.yml

@@ -1,7 +1,7 @@
 title: VProg
 tagline: Competitive programming student club at BME. ICPC, Codeforces, LeetCode, etc.
 description: Competitive programming student club at BME. ICPC, Codeforces, LeetCode, etc.
-avatar: /assets/img/balloons-xmas.png
+avatar: /assets/img/balloons-cartoon.png
 
 social:
   name: VProg