Fix module import path

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

go.mod

@@ -1,4 +1,4 @@
-module github.com/uw-labs/strongbox
+module github.com/uw-labs/strongbox/v2
 
 go 1.21