#119 Fix minor issue in stripe payment

[jkarenzi]

what does this PR do?

• checks the status of the stripe response object, and only changes order.paid to true when the status is succeeded, which implies that the payment is successful. Otherwise an error message is returned

Description of the task to be completed

• add status check before changing order.paid to true
• add new tests to cover added lines

What are the relevant pivotal trackers/story id?

• 119

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.15%. Comparing base (1bf5feb) to head (6f24a83).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #120 +/- ## =========================================== + Coverage 91.14% 91.15% +0.01% =========================================== Files 49 49 Lines 1219 1221 +2 Branches 135 136 +1 =========================================== + Hits 1111 1113 +2 Misses 91 91 Partials 17 17 ```

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