Fix incorrect script id (part 2)

This is a follow-up to 28abadc.

Without the \zs, everything up to the regexp for the script ID would be
used.

Now, s:function() is the same as the one used in scriptease.

autoload/fugitive.vim

@@ -15,7 +15,7 @@ endif
 " Section: Utility
 
 function! s:function(name) abort
-  return function(substitute(a:name,'^s:',matchstr(expand('<sfile>'), '.*<SNR>\d\+_'),''))
+  return function(substitute(a:name,'^s:',matchstr(expand('<sfile>'), '.*\zs<SNR>\d\+_'),''))
 endfunction
 
 function! s:sub(str,pat,rep) abort