Allow newer versions of phpseclib

[magnusnordlander]

Checklists for Pull requests

About pull request itself:

• My changes contain only a single type of change (one bugfix or feature).
• I have read and understood CONTRIBUTING guide

Code Coverage:
(not applicable for non-code fixes of course)

• My pull request has tests that cover 100% of the updated code. (phpunit --coverage-html code-coverage)
• My pull request does not remove any tests that are still needed.

Commits:

• My commits are logical, easily readable, with concise comments.
• My code follows PSR standards of coding style

Licensing:

• I am the author of submission or have been authorized by submission copyright holder to issue this pull request.
• Any new files contain the copyright header directly after the opening <?php line

Branching:

• My submission is based on dev branch
• My submission is compatible with latest master branch updates (no conflicts, I did a rebase if it was necessary).
• The name of the branch I want to merge upstream is not 'master'.
• My branch name follows the pattern feature/some-new-shiny-feature (for new features).
• My branch name follows the pattern bugfix/some-bugfix (for bugfixes).

Continuous integration:

• Once I will submit this pull request, I will wait for Travis-CI report (normally a couple of minutes) and fix any issues I might have introduced.

Pull request description

This PR updates the SDK to allow newer versions of phpseclib. This fixes #144

[magnusnordlander]

Oh, sorry I didn't notice that updating phpseclib was a part of #145. Do with this as you wish then :)

[bretterer]

I like yours better :) This fixes #144