Upgrade recast dev dependency to v0.5.6.

Paving the way for source maps.

package.json

@@ -47,7 +47,7 @@
     "grunt-contrib-jshint": "~0.7.2",
     "optimist": "~0.6.0",
     "phantomjs": "~1.9",
-    "recast": "~0.4.24",
+    "recast": "~0.5.6",
     "semver": "~2.2.1",
     "uglify-js": "~2.4.0",
     "grunt-contrib-clean": "~0.5.0",

vendor/constants.js

@@ -22,7 +22,7 @@ var builders = types.builders;
 var hasOwn = Object.prototype.hasOwnProperty;
 
 function propagate(constants, source) {
-  return recast.print(transform(recast.parse(source), constants));
+  return recast.print(transform(recast.parse(source), constants)).code;
 }
 
 var DEV_EXPRESSION = builders.binaryExpression(