修复webrtc demo网页中stream拼写错误 (#2636)

www/webrtc/index.html

@@ -284,7 +284,7 @@
               ss[o.app].add(o.stream);
               ss[o.app].add(o.stream);
             } else {
             } else {
               let set = new Set();
               let set = new Set();
-              set.add(o.steram);
+              set.add(o.stream);
               ss[o.app] = set;
               ss[o.app] = set;
             }
             }
           }
           }