compute cache salt using package-hash

lib/caching-precompiler.js

@@ -6,6 +6,7 @@ var cachingTransform = require('caching-transform');
 var objectAssign = require('object-assign');
 var stripBom = require('strip-bom');
 var md5Hex = require('md5-hex');
+var packageHash = require('package-hash');
 var enhanceAssert = require('./enhance-assert');
 
 function CachingPrecompiler(cacheDirPath, babelConfig) {
@@ -159,14 +160,11 @@ CachingPrecompiler.prototype._createEspowerPlugin = function () {
 };
 
 CachingPrecompiler.prototype._createTransform = function () {
-	var dependencies = {
-		'babel-plugin-espower': require('babel-plugin-espower/package.json').version,
-		'ava': require('../package.json').version,
-		'babel-core': require('babel-core/package.json').version,
-		'babelConfig': this.babelConfig
-	};
-
-	var salt = new Buffer(JSON.stringify(dependencies));
+	var salt = packageHash.sync([
+		require.resolve('../package.json'),
+		require.resolve('babel-core/package.json'),
+		require.resolve('babel-plugin-espower/package.json')
+	], JSON.stringify(this.babelConfig));
 
 	return cachingTransform({
 		factory: this._factory,

package.json

@@ -124,6 +124,7 @@
     "observable-to-promise": "^0.3.0",
     "only-shallow": "^1.2.0",
     "option-chain": "^0.1.0",
+    "package-hash": "^1.1.0",
     "pkg-conf": "^1.0.1",
     "plur": "^2.0.0",
     "power-assert-formatter": "^1.3.0",