Fix for strong mode error 'Could not infer type parameter E' in upcoming sdk.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135020263
diff --git a/lib/date_symbol_data_http_request.dart b/lib/date_symbol_data_http_request.dart
index deea536..fd4f625 100644
--- a/lib/date_symbol_data_http_request.dart
+++ b/lib/date_symbol_data_http_request.dart
@@ -31,8 +31,10 @@
   var actualLocale = Intl.verifiedLocale(
       locale, (l) => availableLocalesForDateFormatting.contains(l));
   return initializeIndividualLocaleDateFormatting((symbols, patterns) {
-    return Future.wait(
-        [symbols.initLocale(actualLocale), patterns.initLocale(actualLocale)]);
+    return Future.wait(<Future>[
+      symbols.initLocale(actualLocale),
+      patterns.initLocale(actualLocale)
+    ]);
   });
 }