Add strings to forbidden_strings

Message targeted:

```
We have collaborated with OPENSEA on a new free mint. Users in this server can participate.

You can be selected, please participate in CLAIM as soon as possible. some claim might require gas!
```

app.py

@@ -64,7 +64,7 @@ async def on_message(message):
             """Antispam"""
             #Detecting certain unwanted strings
             try:
-                forbidden_strings = ["@everyone", "@here", "discord.gg", "discord.com/invite", "discord.com", "discord-premium"]
+                forbidden_strings = ["@everyone", "@here", "discord.gg", "discord.com/invite", "discord.com", "discord-premium", "opensea", "claim", "mint"]
                 if any(string.lower() in message.content.lower() for string in forbidden_strings):
                     ignored_role_ids = [897381378172264449, 897376942817419265] #admins, huggingfolks
                     if any(role.id in ignored_role_ids for role in message.author.roles):