Fix printing of exact object flow type annotations (#1114)

Fixes #1089.

src/printer.js

@@ -704,10 +704,10 @@ function genericPrintNoParens(path, options, print) {
       if (props.length === 0) {
         return group(
           concat([
-            "{",
+            leftBrace,
             comments.printDanglingComments(path, options),
             softline,
-            "}"
+            rightBrace
           ])
         );
       } else {

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

@@ -0,0 +1,8 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`test.js 1`] = `
+"type Props = {||};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+type Props = {||};
+"
+`;

tests/exact_object/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname);

tests/exact_object/test.js

@@ -0,0 +1 @@
+type Props = {||};