Fixed accidental copy error

Author: Taaku18

app.py

@@ -64,9 +64,9 @@ def strtobool(val):
 @app.listener("before_server_start")
 async def init(app, loop):
     app.ctx.db = AsyncIOMotorClient(MONGO_URI).modmail_bot
-    use_attachment_proxy = strtobool(os.getenv("USE_ATTACHMENT_PROXY", "https://cdn.discordapp.xyz"))
+    use_attachment_proxy = strtobool(os.getenv("USE_ATTACHMENT_PROXY", "no"))
     if use_attachment_proxy:
-        app.ctx.attachment_proxy_url = os.environ["ATTACHMENT_PROXY_URL"]
+        app.ctx.attachment_proxy_url = os.getenv("ATTACHMENT_PROXY_URL", "https://cdn.discordapp.xyz")
         app.ctx.attachment_proxy_url = html.escape(app.ctx.attachment_proxy_url).rstrip("/")
     else:
         app.ctx.attachment_proxy_url = None