Update flow parser to 0.84.0 (#5303)

package.json

@@ -33,7 +33,7 @@
     "esutils": "2.0.2",
     "find-parent-dir": "0.3.0",
     "find-project-root": "1.1.1",
-    "flow-parser": "0.78.0",
+    "flow-parser": "0.84.0",
     "get-stream": "3.0.0",
     "globby": "6.1.0",
     "graphql": "0.13.2",

tests/es6modules/__snapshots__/jsfmt.spec.js.snap

@@ -80,7 +80,7 @@ export default async function foo() {}
 exports[`export_default_function_declaration_async.js - flow-verify 1`] = `
 export default async function foo() {}
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-export default (async function foo() {});
+export default async function foo() {}
 
 `;