Fix await parenthesis (#185)

This is the first time I'm adding something inside of fast-path so I'm not sure if it's correct, but it seems more correct than before!

Fixes #164

src/fast-path.js

@@ -289,6 +289,7 @@ FPp.needsParens = function(assumeExpressionContext) {
           return true;
       }
 
+    case "AwaitExpression":
     case "YieldExpression":
       switch (parent.type) {
         case "BinaryExpression":
@@ -296,13 +297,14 @@ FPp.needsParens = function(assumeExpressionContext) {
         case "UnaryExpression":
         case "SpreadElement":
         case "SpreadProperty":
-        case "CallExpression":
-        case "MemberExpression":
         case "NewExpression":
         case "ConditionalExpression":
-        case "YieldExpression":
+        case "MemberExpression":
           return true;
 
+        case "CallExpression":
+          return parent.callee === node;
+
         default:
           return false;
       }

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

@@ -459,6 +459,13 @@ console.log(x.await);
 
 var await = 3;
 var y = { await };
+
+async function f() { (await f()).length }
+async function g() {
+  invariant(
+    (await driver.navigator.getUrl()).substr(-7)
+  );
+}
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 async function f() {
   await 1;
@@ -514,5 +521,12 @@ console.log(x.await);
 
 var await = 3;
 var y = { await };
+
+async function f() {
+  (await f()).length;
+}
+async function g() {
+  invariant((await driver.navigator.getUrl()).substr(-7));
+}
 "
 `;

tests/async/await_parse.js

@@ -22,3 +22,10 @@ console.log(x.await);
 
 var await = 3;
 var y = { await };
+
+async function f() { (await f()).length }
+async function g() {
+  invariant(
+    (await driver.navigator.getUrl()).substr(-7)
+  );
+}