Copy refinements for tiers

- changed 'Products' to 'Tiers'
- changed 'A segment' to 'Specific tiers'

ghost/admin/app/components/gh-membership-products-alpha.hbs

@@ -1,4 +1,4 @@
-<label>Products</label>
+<label>Tiers</label>
 <div class="gh-product-cards">
 {{#each this.products as |product productIdx|}}
     <div class="gh-product-card">

ghost/admin/app/components/gh-psm-visibility-input.js

@@ -25,7 +25,7 @@ export default Component.extend({
         this.availableVisibilities = VISIBILITIES;
         if (this.feature.get('multipleProducts')) {
             this.availableVisibilities.push(
-                {label: 'A segment', name: 'filter'}
+                {label: 'Specific tier(s)', name: 'filter'}
             );
         }
     },

ghost/admin/app/components/settings/members-default-post-access.js

@@ -30,7 +30,7 @@ export default class SettingsMembersDefaultPostAccess extends Component {
         }];
         if (this.feature.get('multipleProducts')) {
             defaultOptions.push({
-                name: 'A segment',
+                name: 'Specific tier(s)',
                 description: 'Members with any of the selected tiers',
                 value: 'filter',
                 icon: 'members-segment',

ghost/admin/app/controllers/settings/membership.js

@@ -338,7 +338,7 @@ export default class MembersAccessController extends Controller {
             if (this.settings.get('errors').length !== 0) {
                 return;
             }
-            // When no filer is selected in `A Segment` option
+            // When no filer is selected in `Specific tier(s)` option
             if (!this.settings.get('defaultContentVisibility')) {
                 return;
             }