add spec tests for gosec fix

spec/fixtures/gosec/bad_gomod_app/go.mod

@@ -0,0 +1,7 @@
+module test/hello
+
+require (
+	test123.test456.test789/test2 v0.123456
+)
+
+go 1.13

spec/fixtures/gosec/bad_gomod_app/hello.go

@@ -0,0 +1,5 @@
+package hello
+
+func Hello() string {
+	return "Hello!"
+}

spec/fixtures/gosec/bad_gomod_app/hello_test.go

@@ -0,0 +1,10 @@
+package hello
+
+import "testing"
+
+func TestHello(t *testing.T) {
+    want := "Hello!"
+    if got := Hello(); got != want {
+        t.Errorf("Hello() = %q, want %q", got, want)
+    }
+}

spec/lib/salus/scanners/gosec_spec.rb

@@ -6,6 +6,17 @@
 
     before { scanner.run }
 
+    context 'go get ./... fails' do
+      let(:repo) { Salus::Repo.new('spec/fixtures/gosec/bad_gomod_app') }
+
+      it 'should display go get error and not run gosec' do
+        expect(scanner.should_run?).to eq(true)
+        expect(scanner.report.passed?).to eq(false)
+        err_msg = scanner.report.to_h.fetch(:errors).first[:message]
+        expect(err_msg).to include('Unable to start gosec because go get ./... failed.')
+      end
+    end
+
     context 'non-go project' do
       let(:repo) { Salus::Repo.new('spec/fixtures/blank_repository') }