add travis support

[liuchang0812]

travis-ci will run "make check" for any PR and change of leveldb project. I think it's will useful

[liuchang0812]

for example: https://travis-ci.org/Liuchang0812/leveldb/jobs/34773793

[cmumford]

Hi @liuchang0812 I was looking into adding Travis CI and saw your pull request. I'd prefer to give you the credit, but before I can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[ralphtheninja]

+1

[cmumford]

Hi @liuchang0812:

I didn't hear back from you before needing to add support for Travis-CI myself. It was merged in 43fcf23.

[liuchang0812]

@cmumford sorry for this too later replay, i have signed it。