add triple backtick support to ?eval

Author: tinaun

src/main.rs

@@ -127,6 +127,10 @@ fn app() -> Result<()> {
             "?eval mode={} edition={} channel={} ```\ncode```",
             playground::eval,
         );
+        cmds.add(
+            "?eval mode={} edition={} channel={} ```code```",
+            playground::eval,
+        );
         cmds.add(
             "?eval mode={} edition={} channel={} `code`",
             playground::eval,