Add .travis.yml
Set the scheme shared
Specify SDK versions
Update SDK versions

Based on http://blog.travis-ci.com/2014-04-15-xcode-51-ios-71-osx-109/
Force update for xctool
Remove iphonesimulator6.1 from target SDKs

Because tests fails from following error message

```
BTKInjectorDuckTypingTests.m:34:90: error: reference to 'NSNotFound' is ambiguous
        XCTAssertTrue(([exception.reason rangeOfString:@"does not conforms"].location != NSNotFound)
```
Add Travis CI build status image to README
Merge pull request #2 from ikesyo/travis-ci

Set up Travis CI