fix: not throwing error when loading for some languages

Some languages uses comma instead of dot for decimal separator.
When loading vimwiki the following error was occuring
E806: using Float as a String
This is probably a bug in vim, as a workaround when using float can be
str2float.
Similar issue in another project
https://github.com/nathanaelkane/vim-indent-guides/issues/10

plugin/vimwiki.vim

@@ -11,7 +11,7 @@ endif
 let g:loaded_vimwiki = 1
 
 " Set to version number for release, otherwise -1 for dev-branch
-let s:plugin_vers = -1
+let s:plugin_vers = str2float("-1")
 
 " Get the directory the script is installed in
 let s:plugin_dir = expand('<sfile>:p:h:h')