Fix chktex highlighting wrong column when using tabs instead of spaces

Fixes #723

chktex implemented feature request [1] for allowing setting options from
the command line. Thanks to that we can tell it to treat tab character
as of one space width, i.e. one char. That means, after we translate the
output back to Vim columns, we get correct numbers.

[1]: https://savannah.nongnu.org/bugs/?56486

ale_linters/tex/chktex.vim

@@ -16,6 +16,8 @@ function! ale_linters#tex#chktex#GetCommand(buffer) abort
     let l:command = ale#Var(a:buffer, 'tex_chktex_executable')
     " Avoid bug when used without -p (last warning has gibberish for a filename)
     let l:command .= ' -v0 -p stdin -q'
+    " Avoid bug of reporting wrong column when using tabs (issue #723)
+    let l:command .= ' -s TabSize=1'
 
     if !empty(l:chktex_config)
         let l:command .= ' -l ' . ale#Escape(l:chktex_config)