feat: use blake128 instead of md5 to avoid collisions

Author: RisGar

lib/helpers.ml

@@ -23,6 +23,6 @@ let cache_dir =
   dirpath
 
 let get_cache_file file_name cache_type =
-  let hash = Digest.to_hex @@ Digest.MD5.file file_name in
+  let hash = Digest.BLAKE128.to_hex @@ Digest.BLAKE128.file @@ file_name in
 
   cache_dir ^ hash ^ match cache_type with `TEXT -> ".txt" | `THUMB -> ".png"