fix: Correct typo in assertion message (#1904)

Author: josephharrington

lib/chain.js

@@ -80,7 +80,7 @@ Chain.prototype.add = function add(handler) {
             handler.constructor.name,
             'AsyncFunction',
             `Handler [${handlerId}] is missing a third argument (the ` +
-                '"next" callback) but is not an async function. Middlware ' +
+                '"next" callback) but is not an async function. Middleware ' +
                 'handlers can be either async/await or callback-based.' +
                 'Callback-based (non-async) handlers should accept three ' +
                 'arguments: (req, res, next). Async handler functions should ' +
@@ -92,11 +92,11 @@ Chain.prototype.add = function add(handler) {
             handler.constructor.name,
             'AsyncFunction',
             `Handler [${handlerId}] accepts a third argument (the 'next" ` +
-                'callback) but is also an async function. Middlware handlers ' +
-                'can be either async/await or callback-based. Async handler ' +
-                'functions should accept maximum of 2 arguments: (req, res). ' +
-                'Non-async handlers should accept three arguments: (req, ' +
-                'res, next).'
+                'callback) but is also an async function. Middleware ' +
+                'handlers can be either async/await or callback-based. Async ' +
+                'handler functions should accept maximum of 2 arguments: ' +
+                '(req, res). Non-async handlers should accept three ' +
+                'arguments: (req, res, next).'
         );
     }