fix: space in the shared url (#111)

due to the id directly taking in the spaces from the names, the link
shared is containing space in between '%20'. This commit replaces all
the spaces with underscore character in the chapter id.

Co-authored-by: Lukas Klingsbo <[email protected]>

lib/src/story.dart

@@ -399,5 +399,5 @@ class Chapter {
     return story._decorator?.decorate(w) ?? w;
   }
 
-  String get id => '${story.name}_$name';
+  String get id => '${story.name}_$name'.replaceAll(' ', '_');
 }