Update core dependency when updating version (#19)

package.json

@@ -7,6 +7,9 @@
   "dependencies": {
     "bower": "latest"
   },
+  "scripts": {
+    "version": "node update-core-version.js && git add bower.json"
+  },
   "devDependencies": {},
   "keywords": [
     "vaadin",

update-core-version.js

@@ -0,0 +1,8 @@
+var fs = require('fs');
+const fileName = './bower.json';
+var bowerjson = require(fileName);
+
+const version = require('./package.json').version;
+bowerjson.dependencies["vaadin-core"] = version;
+
+fs.writeFileSync(fileName, JSON.stringify(bowerjson, null, 2));