Fix my own typo in helpers.ex

Brand-new language, and I put a ding in it. Sorry about that. :-(

Congratulations on 1.0!

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>
fix previous commit typo bug

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>
Fix a typo in IO.inspect’s doc

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>
Fix a typo in Code.eval_file's doc

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>
Start v1.0.1-dev