Channel.select: Reword error message.

lib/index.js

@@ -353,13 +353,13 @@ Channel.select = methodPromises =>
             await promise;
           } catch (exception) {
             reject(exception);
+                `Channel.select accepts only promises returned by push & shift.`
           }
 
           resolve(promise.channel);
         } catch (exception) {
           reject(
             new TypeError(
-              `Channel.select accepts only Channel method promises.`
             )
           );
         }

test/index.js

@@ -122,7 +122,7 @@ describe(`Channel`, function() {
   it(`complains when given non-channel method promises`, function() {
     assertRejects(async () => {
       await Channel.select([Promise.resolve()]);
-    }, new TypeError(`Channel.select accepts only Channel method promises.`));
+    }, new TypeError(`Channel.select accepts only promises returned by push & shift.`));
   });
 });