Add RNFetchblob.fs.hash function to type definition

[vunyunt]

The RNFetchblob.fs.hash function is missing in the typedef file for typescript, and is added in this PR.

I am aware of the rn-fetch-blob-dev repository but this seems to be a trivial change. Please tell me if I should submit the PR there instead.

PS: This is my first time actually submitting a PR to an open source project, so sorry in advance if there's anything I am doing wrong.

[vunyunt]

When trying to call the function, I get the error

[Info] 01-05 06:53:56.307  5050 10529 I ReactNativeJS: { [TypeError: undefined is not a function (evaluating 'RNFetchBlob.hash(path, algorithm)')]
01-05 06:53:56.307  5050 10529 I ReactNativeJS:   line: 142538,
01-05 06:53:56.307  5050 10529 I ReactNativeJS:   column: 28,`01-05 06:53:56.307  5050 10529 I ReactNativeJS:   sourceURL: 'http://10.0.2.2:8081/index.delta?platform=android&dev=true&minify=false' }

The following is relevant code:

import RNFetchBlob from "rn-fetch-blob";
...
let md5 = await RNFetchBlob.fs.hash(result.path, "md5");
...

Is this an error on my part, either the typedef or the way I am calling it? I don't think it's related to the typedef though, since it seems to be coming from the library itself. Or is the has function not working properly for the current version?

yarn list --pattern=rn-fetch-blob gives me

yarn list v1.12.3
└─ rn-fetch-blob@0.10.15
Done in 0.93s.

[Traviskn]

Thanks for adding the type definition, apologies for the delayed review