[travis] shapeup package.json in release

remove devDependencies from package.json.
resolve #495.

.travis/shapeup.js

@@ -0,0 +1,13 @@
+'use strict'
+
+const fs = require('fs')
+const filename = process.argv[2] || 'package.json'
+
+fs.readFile(filename, (err, data) => {
+    if (err) process.exit(2)
+    const object = JSON.parse(data)
+    delete object.devDependencies
+    fs.writeFile(filename, JSON.stringify(object, null, 4) + '\n', err => {
+        if (err) process.exit(3)
+    })
+})