[travis] shapeup script will indent package.json with tabs

original package.json indented with tabs, but shapeup indent with 4
space.

.travis/shapeup.js

@@ -7,7 +7,7 @@ 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 => {
+    fs.writeFile(filename, JSON.stringify(object, null, '\t') + '\n', err => {
         if (err) process.exit(3)
     })
 })