fix issues proposed

Author: Cheng20010201

config/secrets.exs.example

@@ -0,0 +1,28 @@
+use Mix.Config
+
+config :cadet,
+  luminus: [
+    api_key: "API_KEY",
+    client_id: "CLIENT_ID",
+    client_secret: "CLIENT_SECRET",
+    redirect_url: "REDIRECT_URL"
+  ],
+  updater: [
+    cs1101s_repository: "git@github.com:cs1101s/cs1101s.git",
+    cs1101s_rsa_key: "/home/user/.ssh/cs1101s"
+  ],
+  autograder: [
+    lambda_name: "autograderLambdaName"
+  ],
+  chat: [
+    instance_id: "CHATKIT_INSTANCE_ID",
+    key_id: "CHATKIT_KEY_ID",
+    key_secret: "CHATKIT_KEY_SECRET"
+  ],
+  uploader: [
+    materials_bucket: "env-cadet-materials",
+    sourcecasts_bucket: "env-cadet-sourcecasts"
+  ]
+
+config :sentry,
+  dsn: "https://public_key/sentry.io/somethingsomething"