Update dependencies (#51)

* make specification of versions for packaging and google-cloud-store less strict

Merge pull request #44 from trendelkampschroer/bugix/add_missing_requ…

…ests_dependency

Add missing `requests` dependency.

Merge pull request #43 from trendelkampschroer/bugfix/add_missing_dep…

…endency_specifications

Bugfix/add missing dependency specifications

Merge pull request #42 from trendelkampschroer/bugfix/support_method_…

…whitelist_for_old_urllib3_versions

Bugfix/support method whitelist for old urllib3 versions

expose 'mode' attribute to be compliant with the interface required b…

…y the latest fs version (#40)

Merge pull request #36 from Othoz/cleanup-tests

Remove runtime dependency on NumPy

Retry mechanism (#35)

* Beta version of retry mechanism

* added 502 response code and exponential backoff

* bugfix

* Update CHANGELOG.rst

* fixed tests

* flake8

* Update CHANGELOG.rst

added 502 response code and exponential backoff