add support for prettier-ruby to prettier fixer (#3593)

it _does_ need an additional plugin, but when it has the plugin, it
works as expected.

autoload/ale/fix/registry.vim

@@ -107,7 +107,7 @@ let s:default_registry = {
 \   },
 \   'prettier': {
 \       'function': 'ale#fixers#prettier#Fix',
-\       'suggested_filetypes': ['javascript', 'typescript', 'css', 'less', 'scss', 'json', 'json5', 'graphql', 'markdown', 'vue', 'html', 'yaml', 'openapi'],
+\       'suggested_filetypes': ['javascript', 'typescript', 'css', 'less', 'scss', 'json', 'json5', 'graphql', 'markdown', 'vue', 'html', 'yaml', 'openapi', 'ruby'],
 \       'description': 'Apply prettier to a file.',
 \   },
 \   'prettier_eslint': {

autoload/ale/fixers/prettier.vim

@@ -85,6 +85,7 @@ function! ale#fixers#prettier#ApplyFixForVersion(buffer, version) abort
         \    'yaml': 'yaml',
         \    'openapi': 'yaml',
         \    'html': 'html',
+        \    'ruby': 'ruby',
         \}
 
         for l:filetype in l:filetypes