Merge pull request #1429 from hackmdio/feature/upgrade-markdown-it-10.0.0

feat: upgrade markdown-it to 10.0.0 for supporting em in strong tag

Author: Yukaii

package-lock.json

@@ -82,7 +82,7 @@
     "list.js": "~1.5.0",
     "lodash": "~4.17.15",
     "lutim": "~1.0.2",
-    "markdown-it": "~9.0.1",
+    "markdown-it": "~10.0.0",
     "markdown-it-abbr": "~1.0.4",
     "markdown-it-container": "~2.0.0",
     "markdown-it-deflist": "~2.0.3",