fix exception naming

Author: lohanidamodar

templates/node/index.js.twig

@@ -1,5 +1,5 @@
 const Client = require('./lib/client.js');
-const Client = require('./lib/exception.js');
+const {{spec.title | caseUcfirst}}Exception = require('./lib/exception.js');
 {% for service in spec.services %}
 const {{service.name | caseUcfirst}} = require('./lib/services/{{service.name | caseDash}}.js');
 {% endfor %}