Update parsing of outdated gems

Bundler has changed the way it displays the outdated list. Now it has some output from the sources it is downloading from and then a table with the gems, versions information and other things.

It has been suggested to use the --parseable option to the bundle outdated command. I'm choosing to parse the table output because in the future we want to display version information on commit messages and I think using the table format our lives will be easier.

I chose as separator the line with the table headers to decide that "below" it we'll have the gem list. Seemed better than an fixed number because the lines can vary depending on the gem sources the project uses.

Notice the number of whitespaces can change due to gem names, that's why I remove the whitespaces to make the comparison

Part of #10