Fix handling of monospace font in terminal

src/terminal/index.css

@@ -15,7 +15,7 @@
 
 
 .jp-TerminalWidget-body {
- font-family: "DejaVu Sans Mono", "Liberation Mono", monospace;
+  font-family: monospace;
   outline: none;
   user-select: text;
   -webkit-user-select: text;