`go get` link seems wrong

Here is the install command on the website:
```
go get -u github.com/spf13/cobra/cobra
                                ~~~~~~
```
But that wont work because:
```
go: downloading github.com/spf13/cobra v1.7.0
go: module github.com/spf13/cobra@upgrade found (v1.7.0), but does not contain package github.com/spf13/cobra/cobra
```
Removing the `/cobra` at the end fixes the issue.