feat: upgrade PrismJS, fixed #534

Author: QingWei-Li

package.json

@@ -45,7 +45,7 @@
     "marked": "^0.5.1",
     "medium-zoom": "^0.4.0",
     "opencollective": "^1.0.3",
-    "prismjs": "^1.9.0",
+    "prismjs": "^1.15.0",
     "tinydate": "^1.0.0",
     "tweezer.js": "^1.4.0"
   },