pass build properties from react build

The runReactScript() function should pass on its build properties
so that scripts that follow it can make use of the build info. For
example the createTarFile() function needs this information to
detect if a tar file should be generated.

client/src/react-scripts.js

@@ -128,8 +128,8 @@ function runReactScript(props) {
   };
   return runCommand('node', [`node_modules/react-scripts/scripts/${command}.js`], buildEnv)
     .then((exitCode) => ({
+      ...props,
       now,
-      buildInfo,
       exitCode
     }));
 }