color scale does not work when there is only 1 value

[davelandry]

Expected Behavior

When using the colorScale method, and there is only 1 data point available, the scale gets rendered with no values and the topojson is rendered as black.

Current Behavior

The color scale should not appear, and the topojson should be colored the max color in the scale.

Steps to Reproduce (for bugs)

https://jsfiddle.net/2zb6retc/9/

Your Environment

• Browser Name: Chrome
• Operating System and Version: macOS Sierra