Keep parens around FunctionTypeAnnotation inside ArrayTypeAnnotation (#2561)

Without this, this:

    const actionArray: (() => void)[] = [];

is formatted as:

    const actionArray: () => void[] = [];

Fixes #2559

src/fast-path.js

@@ -458,7 +458,8 @@ FastPath.prototype.needsParens = function(options) {
     case "FunctionTypeAnnotation":
       return (
         parent.type === "UnionTypeAnnotation" ||
-        parent.type === "IntersectionTypeAnnotation"
+        parent.type === "IntersectionTypeAnnotation" ||
+        parent.type === "ArrayTypeAnnotation"
       );
 
     case "StringLiteral":

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

@@ -0,0 +1,8 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`array_of_functions.js 1`] = `
+const actionArray: (() => void)[] = [];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+const actionArray: (() => void)[] = [];
+
+`;

tests/flow_annotation/array_of_functions.js

@@ -0,0 +1 @@
+const actionArray: (() => void)[] = [];

tests/flow_annotation/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, null, ["babylon"]);