Fix 3498 - Change standardrb fixer to read from stdin.

Seems standardrb fails to properly use the --config option when using
temporary files but works fine when reading from stdin. This commit
changes the fixer so it uses stdin instead of temporary files.

autoload/ale/fixers/standardrb.vim

@@ -12,12 +12,12 @@ function! ale#fixers#standardrb#GetCommand(buffer) abort
     return ale#ruby#EscapeExecutable(l:executable, 'standardrb')
     \   . (!empty(l:config) ? ' --config ' . ale#Escape(l:config) : '')
     \   . (!empty(l:options) ? ' ' . l:options : '')
-    \   . ' --fix --force-exclusion %t'
+    \   . ' --fix --force-exclusion --stdin %s'
 endfunction
 
 function! ale#fixers#standardrb#Fix(buffer) abort
     return {
     \   'command': ale#fixers#standardrb#GetCommand(a:buffer),
-    \   'read_temporary_file': 1,
+    \   'process_with': 'ale#fixers#rubocop#PostProcess'
     \}
 endfunction