Replace  with \n in chapter 2
Add newline between </p> and <p>
Translate first section of chapter 2
Update vocabulary
Translate second section of chap2
Update vocabulary
Fix translation of gradient descent
Translate third ant fourth sections of chap2
Update vocabulary
Add name of translator of chapter2
Merge branch 'gh-pages' of github.com:delta2323/nnadl_site_ja into gh-pages