app: fix cgo exported function signature

Fixes a build warning:

android.c:102:44: warning: incompatible pointer types assigning to 'void (*)(ANativeActivity *, int)' (aka 'void (*)(struct ANativeActivity *, int)') from 'void (ANativeActivity *, GoInt)' (aka 'void (struct ANativeActivity *, long long)') [-Wincompatible-pointer-types]

Change-Id: Ib70bcf8a8e32bb1885ec809d239199fccb1dc4fa
Reviewed-on: https://go-review.googlesource.com/128235
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/app/android.go b/app/android.go
index b6402e0..213e31d 100644
--- a/app/android.go
+++ b/app/android.go
@@ -137,7 +137,7 @@
 }
 
 //export onWindowFocusChanged
-func onWindowFocusChanged(activity *C.ANativeActivity, hasFocus int) {
+func onWindowFocusChanged(activity *C.ANativeActivity, hasFocus C.int) {
 }
 
 //export onNativeWindowCreated