changed require() to import

src/HtmlUtils.tsx

@@ -17,8 +17,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-require('katex/dist/katex.min.css');
-
 import React from 'react';
 import sanitizeHtml from 'sanitize-html';
 import * as linkify from 'linkifyjs';
@@ -29,6 +27,7 @@ import classNames from 'classnames';
 import EMOJIBASE_REGEX from 'emojibase-regex';
 import url from 'url';
 import katex from 'katex';
+import 'katex/dist/katex.min.css';
 import { AllHtmlEntities } from 'html-entities';
 import SdkConfig from './SdkConfig';