fix: skip history if empty input

src/simple_repl.gleam

@@ -55,11 +55,18 @@ fn append_history(cmd: String) -> Nil {
 fn repl_loop(cmds: dict.Dict(String, fn() -> Nil)) -> a {
   let input = get_line("repl> ") |> string.trim
   let cmd = string.lowercase(input)
-  input |> append_history
-  case dict.get(cmds, cmd) {
-    Ok(func) -> func()
-    Error(_) -> io.println(input <> ": unknown command")
+
+  case cmd {
+    "" -> Nil
+    _ -> {
+      input |> append_history
+      case dict.get(cmds, cmd) {
+        Ok(func) -> func()
+        Error(_) -> io.println(input <> ": unknown command")
+      }
+    }
   }
+
   repl_loop(cmds)
 }