Add @ember/string to ember-try scenarios to get newer ember scenarios

passing

Author: kategengler

config/ember-try.js

@@ -66,6 +66,7 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': await getChannelURL('release'),
+            '@ember/string': '^3.1.1',
           },
           ember: {
             edition: 'octane',
@@ -77,6 +78,7 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': await getChannelURL('beta'),
+            '@ember/string': '^3.1.1',
           },
           ember: {
             edition: 'octane',
@@ -88,6 +90,7 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': await getChannelURL('canary'),
+            '@ember/string': '^3.1.1',
           },
           ember: {
             edition: 'octane',