Turn on flow for scripts/start.js (#242)

Summary:
  - The value of `process.stdout.isTTY` is either `true` or `undefined`.
    Flow (reasonably) dislikes this, so we add an explicit check.
  - More `package.json` burnination.

Test Plan:
Note that `require("./package.json").proxy === undefined` in the Node
console, and that `yarn start` works.

wchargin-branch: flow--scripts-start

scripts/start.js

@@ -1,4 +1,4 @@
-// @no-flow
+// @flow
 "use strict";
 
 // Do this as the first thing so that any code reading it knows the right env.
@@ -33,7 +33,8 @@ const config = require("../config/webpack.config.dev");
 const createDevServerConfig = require("../config/webpackDevServer.config");
 
 const useYarn = fs.existsSync(paths.yarnLockFile);
-const isInteractive = process.stdout.isTTY;
+const isInteractive =
+  typeof process.stdout.isTTY !== "undefined" && process.stdout.isTTY;
 
 // Warn and crash if required files are missing
 if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
@@ -68,12 +69,12 @@ choosePort(HOST, DEFAULT_PORT)
       return;
     }
     const protocol = process.env.HTTPS === "true" ? "https" : "http";
-    const appName = require(paths.appPackageJson).name;
+    const appName = "sourcecred";
     const urls = prepareUrls(protocol, HOST, port);
     // Create a webpack compiler that is configured with custom messages.
     const compiler = createCompiler(webpack, config, appName, urls, useYarn);
     // Load proxy config
-    const proxySetting = require(paths.appPackageJson).proxy;
+    const proxySetting = undefined;
     const proxyConfig = prepareProxy(proxySetting, paths.appPublic);
     // Serve webpack assets generated by the compiler over a web sever.
     const serverConfig = createDevServerConfig(