Add static interface implementation check

Add an additional line of code per interface to the generated mock file,
which allows the go compiler to statically check if the mock implements
the mocked interface.

pkg/moq/testpackages/dotimport/service_moq_test.go

@@ -12,6 +12,10 @@ var (
 	lockServiceMockUser sync.RWMutex
 )
 
+// Ensure, that ServiceMock does implement Service.
+// If this is not the case, regenerate this file with moq.
+var _ dotimport.Service = &ServiceMock{}
+
 // ServiceMock is a mock implementation of Service.
 //
 //     func TestSomethingThatUsesService(t *testing.T) {