cfgparse: be forgiving about a missing "ms" after a duration

While it’s certainly better and clearer to specify it, we should do the
right thing when the unit is missing, just like CSS for example
(margin: 0; is okay, margin: 0px; too).

src/cfgparse.y

@@ -1057,7 +1057,8 @@ word_or_number:
     ;
 
 duration:
-    NUMBER TOK_TIME_MS { sasprintf(&$$, "%d", $1); }
+    NUMBER { sasprintf(&$$, "%d", $1); }
+    | NUMBER TOK_TIME_MS { sasprintf(&$$, "%d", $1); }
     ;
 
 mode: