added filename to stdin stream of isort (#3815)

modified tests to run with new format

Co-authored-by: Jeff Willette <jeff@Jeffs-MacBook-Pro.local>

autoload/ale/fixers/isort.vim

@@ -29,6 +29,7 @@ function! ale#fixers#isort#Fix(buffer) abort
     return {
     \   'cwd': '%s:h',
     \   'command': ale#Escape(l:executable) . l:exec_args
+    \   . ale#Pad('--filename %s')
     \   . (!empty(l:options) ? ' ' . l:options : '') . ' -',
     \}
 endfunction