Tidy up some build logs (facebook#2197)

Author: gaearon

config/webpack.config.prod.js

@@ -305,6 +305,13 @@ module.exports = {
       // about it being stale, and the cache-busting can be skipped.
       dontCacheBustUrlsMatching: /\.\w{8}\./,
       filename: 'service-worker.js',
+      logger(message) {
+        if (message.indexOf('Total precache size is') === 0) {
+          // This message occurs for every build and is a bit too noisy.
+          return;
+        }
+        console.log(message);
+      },
       minify: true,
       navigateFallback: publicUrl + '/index.html',
       staticFileGlobsIgnorePatterns: [/\.map$/, /asset-manifest\.json$/],