[e.cash] Naming tweak for fetch blog function

Summary:
Im working on the blog page and realized the return value of the getBlogPosts function could be named better, 'posts'
makes more sense than 'responses' to me. Also realized the propsObj props value needs to be an object to work with getStaticProps

Test Plan: npm run test should still pass

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14137