Support different ways to import gomega

[nunnatsa]

ginkgo documentation uses dot import; i.e.

import . "github.com/onsi/gomega"

But the user can use impot without name or with custom name, e.g.

import "github.com/onsi/gomega"

Or

import custom "github.com/onsi/gomega"

This PR adds support for these two forms of importt.

Also, the linter now skips files without gomega import.