Update .travis.yml
Update .travis.yml

added arch attribute on YML file.
huycn/zxing-cpp,nu-book/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,huycn/zxing-cpp,huycn/zxing-cpp