更新 placeholder_images.yaml

add more random cover

Author: IMZCC

data/placeholder_images.yaml

@@ -21,3 +21,8 @@ images:
   - "https://t.alcy.cc/moe?random=13"
   - "https://t.alcy.cc/moe?random=14"
   - "https://t.alcy.cc/moe?random=15"
+  - "https://t.alcy.cc/moe?random=16"
+  - "https://t.alcy.cc/moe?random=17"
+  - "https://t.alcy.cc/moe?random=18"
+  - "https://t.alcy.cc/moe?random=19"
+  - "https://t.alcy.cc/moe?random=20"