Change dependency react-native-fetch-blob to rn-fetch-blob as the previous repo has been achieved

[sam17896]

Hello, I am using this package with RN 0.60, and i am getting error RNFetchBlob.DocumentDIr undefined i think the cause of this issue is that react-native-fetch-blob has been deprecated in favour of rn-fetch-blob, this package should use the updated package.

[kirillrevasiliev]

have the same issue after upgrade to RN .60

[mayconmesquita]

rn-fetch-blob is updated, please update this dependency.