concat: Fix Wallaby.js bug.

lib/index.js

@@ -112,9 +112,23 @@ const Channel = function(length = 0) {
           for (let index = 0; index < args.length; index++) {
             const arg = args[index];
 
-            await (Channel.isChannel(arg)
+            /* For some reason the following code works in Mocha but not in
-              ? arg.forEach(output.push)
+              Wallaby.js:
-              : output.push(arg));
+
+              await (Channel.isChannel(arg)
+                ? arg.forEach(output.push)
+                : output.push(arg));
+
+              If we use the 'if' statement below then Wallaby.js is happy.
+            */
+
+            if (Channel.isChannel(arg)) {
+              await arg.forEach(value => {
+                output.push(value);
+              });
+            } else {
+              await output.push(arg);
+            }
           }
 
           output.close();