Twitter icon click results in 404
### Bug report
Within README.md, 
is displayed using this code:
[![Twitter Follow](https://img.shields.io/twitter/follow/davidwilliames.svg?style=social&label=Follow)]()
#### Expected behavior:
Clicking on the icon should bring me to Twitter.com
#### Actual behavior:
But clicking on the 
![image](https://user-images.githubusercontent.com/300046/43287021-f7ae1b92-90e0-11e8-8fe3-067f99872568.png)
results in a 404.
Analysis: The link itself, when pasted in a browser brings me to Twitter.
