changed css property

[kambayashia]

'background:' overwrite many properties.

before

.class-name {
    background: url('data:image/png;.....');
}

after

.class-name {
    background-image: url('data:image/png;.....');
}

[heldr]

Hi, could you please update the tests?

https://travis-ci.org/heldr/datauri/jobs/61119118

[kambayashia]

👌

[coveralls]

Coverage remained the same at 100.0% when pulling 1c929f1 on kambayashia:master into 089ab07 on heldr:master.

[kambayashia]

updated test.

[heldr]

Thanks for the contribution 🍵

[kambayashia]

👍