Update build.gradle

ios/build.gradle

@@ -8,6 +8,7 @@ ext{
 }
 
 task copyAssets(){
+    doLast{
     delete{
         delete "assets/"
     }
@@ -30,6 +31,7 @@ task copyAssets(){
             include '**/*.ogg'
         }
     }
+    }
 }
 
 createIPA.dependsOn copyAssets
@@ -44,4 +46,4 @@ createIPA.dependsOn build
 
 robovm{
     archs = "thumbv7:arm64"
-}
+}