Update go module url

It looks like the go module is now at `go get github.com/segmentio/analytics-go/v3`

Following the docs a user gets this warning:

```
% go get gopkg.in/segmentio/analytics-go.v3

go: downloading gopkg.in/segmentio/analytics-go.v3 v3.2.1
go: gopkg.in/segmentio/[email protected]: parsing go.mod:
	module declares its path as: github.com/segmentio/analytics-go/v3
	        but was required as: gopkg.in/segmentio/analytics-go.v3
```

Author: nzoschke

src/connections/sources/catalog/libraries/server/go/quickstart.md

@@ -27,7 +27,7 @@ When you create a Source in the Segment web app, it tells the Segment servers th
 Installing our Go library is easy, just run the following:
 
 ```bash
-go get gopkg.in/segmentio/analytics-go.v3
+go get github.com/segmentio/analytics-go/v3
 ```
 
 Then just import the library and initialize a new client your Segment source's **Write Key**, like so: