Fix regression caused by using newer version of Grape

This commit fixes the regression caused by using a newer version of Grape and Grape entity.  This solves Issue #4023.

I don't know if there was a particular reason for changing Grape version (commit 083d66563e8275fd13851ec0a1974cb17379f84f). If there is no compelling reason to change the Grape version, I recommend we revert that change with this PR to solve the current regression with raw content in the API.  This regression breaks tools that integrate with the API.

Before:
![before](https://f.cloud.github.com/assets/2394772/564751/7d1e10f2-c59e-11e2-93c4-7711f6db3151.png)

After:
![after](https://f.cloud.github.com/assets/2394772/564744/f8f7ae46-c59d-11e2-933b-4d9deafa360a.png)