BUILD.gn: Fix formatting.

Bug: skia:9713
Change-Id: Ief84ae139acd000b29adcf32e0aead2fbdbff166
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/259536
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>

Author: HalCanary

experimental/skottie_ios/BUILD.gn

@@ -7,9 +7,9 @@ import("../../gn/ios.gni")
 if (is_ios) {
   ios_app_bundle("skottie_ios") {
     sources = [
-      "main.mm",
       "SkAnimationDraw.h",
       "SkTimeKeeper.h",
+      "main.mm",
     ]
     if (skia_use_metal) {
       sources += [