Added text/javascript as a possible content-type response to the _validate method

pkg/oauth2/lib/src/handle_access_token_response.dart

Index: pkg/oauth2/lib/src/handle_access_token_response.dart
diff --git a/pkg/oauth2/lib/src/handle_access_token_response.dart b/pkg/oauth2/lib/src/handle_access_token_response.dart
index 129f259194bfdb4a61881504fc0b015683c73590..eb219d7a90db46486301f9256882970aa7334c9d 100644
--- a/pkg/oauth2/lib/src/handle_access_token_response.dart
+++ b/pkg/oauth2/lib/src/handle_access_token_response.dart
@@ -34,8 +34,8 @@ Credentials handleAccessTokenResponse(
   if (contentType != null) {
     contentType = ContentType.parse(contentType);
   }
-  validate(contentType != null && contentType.value == "application/json",
-      'content-type was "$contentType", expected "application/json"');
+  validate(contentType != null && (contentType.value == "application/json" || contentType.value == "text/javascript"),
+      'content-type was "$contentType", expected "application/json" or "text/javascript"');
 
   var parameters;
   try {