Fix #735 - Support old versions of Flow by only adding --respect-pragma for supported versions

autoload/ale/engine.vim

@@ -387,6 +387,16 @@ function! s:RunJob(options) abort
         let l:read_buffer = 0
     endif
 
+    " Add a newline to commands which need it.
+    " This is only used for Flow for now, and is not documented.
+    if l:linter.add_newline
+        if has('win32')
+            let l:command = l:command . '; echo.'
+        else
+            let l:command = l:command . '; echo'
+        endif
+    endif
+
     let l:command = ale#job#PrepareCommand(l:command)
     let l:job_options = {
     \   'mode': 'nl',

autoload/ale/linter.vim

@@ -50,6 +50,7 @@ function! ale#linter#PreProcess(linter) abort
     endif
 
     let l:obj = {
+    \   'add_newline': get(a:linter, 'add_newline', 0),
     \   'name': get(a:linter, 'name'),
     \   'lsp': get(a:linter, 'lsp', ''),
     \}