agdk-mainloop: fix features declaration

Author: rib

examples/agdk-mainloop/Cargo.toml

@@ -8,7 +8,7 @@ edition = "2021"
 [dependencies]
 log = "0.4"
 android_logger = "0.11.0"
-android-activity = { path="../../android-activity", features = "game-activity" }
+android-activity = { path="../../android-activity", features = ["game-activity"] }
 
 [lib]
 name="main"