fixed error message

service/http_json.js

@@ -22,7 +22,7 @@ function synthesizeUrl(serviceConfig, req) {
 
 module.exports = function setup(serviceConfig) {
   if (!(serviceConfig instanceof ServiceConfiguration)) {
-    throw Error('serviceConfig be an instance of ServiceConfiguration');
+    throw Error('serviceConfig should be an instance of ServiceConfiguration');
   }
 
   if (_.isEmpty(serviceConfig.getBaseUrl())) {

test/unit/service/http_json.js

@@ -25,7 +25,7 @@ module.exports.tests.conforms_to = (test, common) => {
   test('non-ServiceConfiguration instance should throw error', (t) => {
     const serviceConfig = 'not an instance of serviceConfiguration';
 
-    t.throws(setup.bind(null, serviceConfig), /serviceConfig be an instance of ServiceConfiguration/);
+    t.throws(setup.bind(null, serviceConfig), /serviceConfig should be an instance of ServiceConfiguration/);
     t.end();
 
   });