not able to build gocql in docker environment from v1.20 onwards

Please answer these questions before submitting your issue. Thanks!

### What version of Cassandra are you using?
cassandra 3.1.0

### What version of Gocql are you using?
v1.2.0

### What version of Go are you using?
1.15.0

### What did you do?
i want to install gocl in a docker environment in amd64. this is my docker file
```
FROM amd64/golang:1.15.0

RUN apt-get update
RUN GO111MODULE=on GOPATH= go get "github.com/gocql/gocql@v1.2.0"
```

### What did you expect to see?
I expected it to be installed fine

### What did you see instead?

```
Sending build context to Docker daemon 20.04MB
Step 1/3 : FROM amd64/golang:1.15.0
---> 166f2b5fae2d
Step 2/3 : RUN apt-get update
---> Running in cf41d0151dd7
Get:1 http://security.debian.org/debian-security buster/updates InRelease [34.8 kB]
Get:2 http://deb.debian.org/debian buster InRelease [122 kB]
Get:3 http://deb.debian.org/debian buster-updates InRelease [56.6 kB]
Get:4 http://security.debian.org/debian-security buster/updates/main amd64 Packages [348 kB]
Get:5 http://deb.debian.org/debian buster/main amd64 Packages [7911 kB]
Get:6 http://deb.debian.org/debian buster-updates/main amd64 Packages [8788 B]
Fetched 8481 kB in 3s (2890 kB/s)
Reading package lists...
Removing intermediate container cf41d0151dd7
---> 9a1f9eb88752
Step 3/3 : RUN GO111MODULE=on GOPATH= go get "github.com/gocql/gocql@v1.2.0"
---> Running in 8b566af4757f
go: downloading github.com/gocql/gocql v1.2.0
go: downloading github.com/golang/snappy v0.0.3
go: downloading gopkg.in/inf.v0 v0.9.1
go: downloading github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed
# github.com/gocql/gocql
/root/go/pkg/mod/github.com/gocql/gocql@v1.2.0/dial.go:79:18: tconn.HandshakeContext undefined (type *tls.Conn has no field or method HandshakeContext)

```

---

If you are having connectivity related issues please share the following additional information

NA

### Describe your Cassandra cluster
please provide the following information

- output of `nodetool status`
- output of `SELECT peer, rpc_address FROM system.peers`
- rebuild your application with the `gocql_debug` tag and post the output

Reproduce the Dockerfile command with the amd64/golang:1.15.0 image and gocql v1.2.0. Inspect dial.go at line 79 and the reported tls.Conn HandshakeContext error. Done means the stated Docker build completes successfully for github.com/gocql/gocql@v1.2.0.

Written by the indexing model from the issue text.