Update CodeMirror to version 5.48.4 (jupyter#4858)

The current CodeMirror version incorrectly highlights 
f-formatted strings which is fixed on latest CodeMirror
version.

Fixes jupyter#4854

Author: bermani

bower.json

@@ -5,7 +5,7 @@
     "backbone": "components/backbone#~1.2",
     "bootstrap": "bootstrap#~3.4",
     "bootstrap-tour": "0.9.0",
-    "codemirror": "components/codemirror#~5.37",
+    "codemirror": "components/codemirror#~5.48.4",
     "create-react-class": "https://cdn.jsdelivr.net/npm/[email protected]/create-react-class.min.js",
     "es6-promise": "~1.0",
     "font-awesome": "components/font-awesome#~4.7.0",