### What it does
Checks to see if multiple versions of a crate are being
used.

### Why is this bad?
This bloats the size of targets, and can lead to
confusing error messages when structs or traits are used interchangeably
between different versions of a crate.

### Known problems
Because this can be caused purely by the dependencies
themselves, it's not always possible to fix this issue.

### Example
```
[dependencies]
ctrlc = "=3.1.0"
ansi_term = "=0.11.0"
```