Update dependencies to newest working versions

[randyzwitch]

In merging #32, dependencies are pinned on some very old versions of npm packages. Specifically, mapd-connector is pinned to right before v3.0.0, which had breaking changes. mapd-connector at the time of this issue is at version 4.2.0, indicating that it's likely that additional breaking changes have occurred.

In evaluating what it would take to update Tweetmap 2 to newest versions, there are a handful of high-level projects:

• Update mapd-connector and related libraries to their newest versions
• Updating React from v15 to v16
• Updating webpack from v2 to v4
• Update other dependencies for security and/or functionality improvements

Using yarn upgrade-interactive, many updates to other dependencies could be done without the major overhauls identified in the first 3 bullet points above.