Reformat CSV timestamp to officially supported format

[caseycesari]

Overview

The provided format can be parsed in Chrome, but not Safari, which is the target device for the app.

The solution is from https://stackoverflow.com/a/5646753

Connects #84

Testing Instructions

• Visit the Delaware River sensor in both Chrome and Safari, and verify that the app works in both cases.

[caseycesari]

Thanks!