Add `optionalChaining` as a valid babylon plugin option to flow typing

Reviewed By: rafeca

Differential Revision: D7828243

fbshipit-source-id: 8b3cbaa8efb0f91263b3b09cbe012f8a5d8bfdbe

flow-typed/babel.js.flow

@@ -26,17 +26,18 @@ type BabylonOptions = {
   sourceType?: 'script' | 'module',
   sourceFilename?: 'string',
   plugins?: Array<
-    | 'jsx'
-    | 'flow'
-    | 'doExpressions'
-    | 'objectRestSpread'
-    | 'decorators'
-    | 'classProperties'
-    | 'exportExtensions'
     | 'asyncGenerators'
+    | 'classProperties'
+    | 'decorators'
+    | 'doExpressions'
+    | 'dynamicImport'
+    | 'exportExtensions'
+    | 'flow'
     | 'functionBind'
     | 'functionSent'
-    | 'dynamicImport',
+    | 'jsx'
+    | 'objectRestSpread'
+    | 'optionalChaining',
   >,
 };