Fix command push
Fix command push

- push was using 'exec' to call bash commands
but this function call the bash command into
another process and never back to the ruby
process.

- I change to use the function 'system' for
each bash function, because this function
call the bash command into another process
and before returns to the ruby process

lemurheavy/coveralls-ruby,sferik/coveralls-ruby,tagliala/coveralls-ruby