Fix linting errors

refs https://github.com/TryGhost/Ghost-Admin/pull/1274

- fixes errors introduced from upgrading to eslint@6

ghost/admin/app/components/gh-image-uploader.js

@@ -122,7 +122,6 @@ export default Component.extend({
         fileSelected(fileList, resetInput) {
             // can't use array destructuring here as FileList is not a strict
             // array and fails in Safari
-            // eslint-disable-next-line ember-suave/prefer-destructuring
             let file = fileList[0];
             let validationResult = this._validate(file);
 

ghost/admin/app/controllers/editor.js

@@ -772,7 +772,6 @@ export default Controller.extend({
         let errorMessage;
 
         function isString(str) {
-            /* global toString */
             return toString.call(str) === '[object String]';
         }
 

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

@@ -296,11 +296,7 @@ export default Controller.extend({
     }).drop(),
 
     saveSettings: task(function* () {
-        try {
-            return yield this.settings.save();
-        } catch (error) {
-            throw error;
-        }
+        return yield this.settings.save();
     }).drop(),
 
     redirectUploadResult: task(function* (success) {

ghost/admin/app/utils/password-generator.js

@@ -15,7 +15,7 @@ function rand(min, max) {
     var key, value, arr = new Uint8Array(max);
     getRandomValues(arr);
     for (key in arr) {
-        if (arr.hasOwnProperty(key)) {
+        if (Object.prototype.hasOwnProperty.call(arr, key)) {
             value = arr[key];
             if (value > min && value < max) {
                 return value;

ghost/admin/mirage/config/authentication.js

@@ -10,7 +10,6 @@ export default function mockAuthentication(server) {
 
     server.post('/authentication/passwordreset', function (schema, request) {
         let {passwordreset} = JSON.parse(request.requestBody);
-        // eslint-disable-next-line ember-suave/prefer-destructuring
         let email = passwordreset[0].email;
 
         if (email === 'unknown@example.com') {