fix fastboot styles reloading

lib/broccoli/fastboot-config.js

@@ -1,6 +1,7 @@
 var fs     = require('fs');
 var fmt    = require('util').format;
 var uniq   = require('lodash.uniq');
+var md5Hex = require('md5-hex');
 var path   = require('path');
 var Plugin = require('broccoli-plugin');
 
@@ -15,6 +16,7 @@ function FastBootConfig(inputNode, options) {
   this.fastbootAppConfig = options.fastbootAppConfig;
   this.outputPaths = options.outputPaths;
   this.appConfig = options.appConfig;
+  this._fileToChecksumMap = {};
 }
 
 FastBootConfig.prototype = Object.create(Plugin.prototype);
@@ -31,7 +33,17 @@ FastBootConfig.prototype.build = function() {
   this.buildHostWhitelist();
 
   var outputPath = path.join(this.outputPath, 'package.json');
-  fs.writeFileSync(outputPath, this.toJSONString());
+  this.writeFileIfContentChanged(outputPath, this.toJSONString());
+};
+
+FastBootConfig.prototype.writeFileIfContentChanged = function(outputPath, content) {
+  var previous = this._fileToChecksumMap[outputPath];
+  var next = md5Hex(content);
+
+  if (previous !== next) {
+    fs.writeFileSync(outputPath, content);
+    this._fileToChecksumMap[outputPath] = next; // update map
+  }
 };
 
 FastBootConfig.prototype.buildDependencies = function() {

package.json

@@ -76,6 +76,7 @@
     "fastboot-filter-initializers": "0.0.2",
     "lodash.defaults": "^4.0.1",
     "lodash.uniq": "^4.2.0",
+    "md5-hex": "^1.3.0",
     "portfinder": "^1.0.3",
     "rsvp": "^3.0.16",
     "silent-error": "^1.0.0"