Fix module import path

[matthewhughes-uw]

I was trying to install this and running into errors:

$ go install github.com/uw-labs/[email protected]
go: github.com/uw-labs/[email protected]: github.com/uw-labs/[email protected]: invalid version: module contains a go.mod file, so module path must match major version ("github.com/uw-labs/strongbox/v2")
$ go install github.com/uw-labs/strongbox/[email protected]
go: github.com/uw-labs/strongbox/[email protected]: github.com/uw-labs/[email protected]: invalid version: module contains a go.mod file, so module path must match major version ("github.com/uw-labs/strongbox/v2")

Resolve these by adding the major version to the module path

[matthewhughes-uw]

testing (git SHA is from commit on this PR):

$ go install github.com/uw-labs/strongbox@66c63e99510b49ba879582cf7975492f9b81dd9c
go: github.com/uw-labs/strongbox@66c63e99510b49ba879582cf7975492f9b81dd9c: github.com/uw-labs/[email protected]: invalid version: go.mod has post-v1 module path "github.com/uw-labs/strongbox/v2" at revision 66c63e99510b
$ go install -x github.com/uw-labs/strongbox/v2@66c63e99510b49ba879582cf7975492f9b81dd9c
$ echo $?
0