Update Install_rails.sh

fixed rdoc and other install errors.
Example:
unable to convert "\x89" from ASCII-8BIT to UTF-8 for guides/assets/images/rails4_features.png, skipping
unable to convert "\xFF" from ASCII-8BIT to UTF-8 for guides/assets/images/rails_guides_kindle_cover.jpg, skipping
unable to convert "\xEC" from ASCII-8BIT to UTF-8 for guides/assets/images/rails_guides_logo.gif, skipping
unable to convert "\x8C" from ASCII-8BIT to UTF-8 for guides/assets/images/rails_logo_remix.gif, skipping
unable to convert "\x89" from ASCII-8BIT to UTF-8 for guides/assets/images/session_fixation.png, skipping
unable to convert "\x80" from ASCII-8BIT to UTF-8 for guides/assets/images/tab_grey.gif, skipping
unable to convert "\x80" from ASCII-8BIT to UTF-8 for guides/assets/images/tab_info.gif, skipping
unable to convert "\x80" from ASCII-8BIT to UTF-8 for guides/assets/images/tab_note.gif, skipping
unable to convert "\x80" from ASCII-8BIT to UTF-8 for guides/assets/images/tab_red.gif, skipping
unable to convert "\x80" from ASCII-8BIT to UTF-8 for guides/assets/images/tab_yellow.gif, skipping
unable to convert "\x89" from ASCII-8BIT to UTF-8 for guides/assets/images/tab_yellow.png, skipping
unable to convert "\xFF" from ASCII-8BIT to UTF-8 for guides/assets/images/vijaydev.jpg, skipping