Update tests to use TravisCI

This will remove the current .drone.yml which isn't used anymore, update the
Makefile target and move tests to using `t.Skip` instead of `t.Fatal` if no
database exists during tests. This is so it's possible to develop new tests
that may not require a database.

cleanup_test.go

@@ -10,7 +10,7 @@ import (
 func TestCleanup(t *testing.T) {
 	ss := NewPGStore(os.Getenv("PGSTORE_TEST_CONN"), []byte(secret))
 	if ss == nil {
-		t.Fatal("This test requires a real database")
+		t.Skip("This test requires a real database")
 	}
 
 	defer ss.Close()