Remove use of optional chaining in client (#253)

Author: mattt

index.js

@@ -163,15 +163,15 @@ class Replicate {
         }
 
         // We handle the cancel later in the function.
-        if (signal?.aborted) {
+        if (signal && signal.aborted) {
           return true; // stop polling
         }
 
         return false; // continue polling
       }
     );
 
-    if (signal?.aborted) {
+    if (signal && signal.aborted) {
       prediction = await this.predictions.cancel(prediction.id);
     }