Fix #1424 - Make the brittany fixer work

autoload/ale/fixers/brittany.vim

@@ -1,4 +1,4 @@
-" Author: eborden <evan@evan-borden.com>
+" Author: eborden <evan@evan-borden.com>, ifyouseewendy <ifyouseewendy@gmail.com>, aspidiets <emarshall85@gmail.com>
 " Description: Integration of brittany with ALE.
 
 call ale#Set('haskell_brittany_executable', 'brittany')
@@ -8,6 +8,7 @@ function! ale#fixers#brittany#Fix(buffer) abort
 
     return {
     \   'command': ale#Escape(l:executable)
+    \       . ' --write-mode inplace'
     \       . ' %t',
     \   'read_temporary_file': 1,
     \}

test/fixers/test_brittany_fixer_callback.vader

@@ -18,6 +18,7 @@ Execute(The brittany callback should return the correct default values):
   \ {
   \   'read_temporary_file': 1,
   \   'command': ale#Escape('xxxinvalid')
+  \     . ' --write-mode inplace'
   \     . ' %t',
   \ },
   \ ale#fixers#brittany#Fix(bufnr(''))