Fix in inside of the first group of a for (#406)

Fixes #405

src/fast-path.js

@@ -267,6 +267,10 @@ FPp.needsParens = function(assumeExpressionContext) {
       }
 
     case "BinaryExpression":
+      if (node.operator === "in" && parent.type === "ForStatement" && parent.init === node) {
+        return true;
+      }
+
     case "LogicalExpression":
       switch (parent.type) {
         case "CallExpression":

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

@@ -292,6 +292,14 @@ for (var i = 0; i < 10; ++i) {
 "
 `;
 
+exports[`test in.js 1`] = `
+"for ((x in a);;) {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+for ((x in a); ; ) {
+}
+"
+`;
+
 exports[`test var.js 1`] = `
 "for (a in b) var c = {}; [];
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

tests/for/in.js

@@ -0,0 +1 @@
+for ((x in a);;) {}