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.

.travis.yml

@@ -0,0 +1,18 @@
+language: go
+
+go:
+  - 1.2
+  - tip
+
+script: make test
+
+env:
+  - PGSTORE_TEST_CONN="postgres://postgres@127.0.0.1/test?sslmode=disable"
+
+before_script:
+  - psql -c 'create database test;' -U postgres
+
+addons:
+  postgresql: "9.3"
+
+sudo: false