Use the correct name of the binary encoding selector

[cameel]

The library currently calls hash.digest('bin') which crashes browserify-sha3.

hash is either the C implementation which comes from sha3 package (when available) or the JS one from browserify-sha3 otherwise. The latter clearly expects the value to be 'binary', not 'bin'. Same for sha3 but it's more lax and just assumes 'binary' when the encoding is not recognized.

I'm not sure how to write a test for this but I checked it manually and 'binary' works with both.

Error output

I got this in ethereum/solc-bin#40. Apparently sha3 must have failed to build in Travis and it fell back to browserify-sha3: https://travis-ci.org/github/ethereum/solc-bin/builds/744413140

Computing hashes of '/linux-amd64/solc-linux-amd64-v0.4.10+commit.f0d539ae'
/home/travis/build/ethereum/solc-bin/node_modules/browserify-sha3/index.js:32
    throw new Error('Unsupported encoding for digest: ' + encoding)
          ^

Error: Unsupported encoding for digest: bin
    at hash.digest (/home/travis/build/ethereum/solc-bin/node_modules/browserify-sha3/index.js:32:11)
    at swarmHashBlock (/home/travis/build/ethereum/solc-bin/node_modules/swarmhash/index.js:11:27)
    at swarmHash (/home/travis/build/ethereum/solc-bin/node_modules/swarmhash/index.js:18:12)
    at swarmHash (/home/travis/build/ethereum/solc-bin/node_modules/swarmhash/index.js:29:21)
    at swarmHash (/home/travis/build/ethereum/solc-bin/node_modules/swarmhash/index.js:29:21)
    at makeEntry (/home/travis/build/ethereum/solc-bin/update:143:19)
    at async /home/travis/build/ethereum/solc-bin/update:193:43
    at async Promise.all (index 0)
    at async /home/travis/build/ethereum/solc-bin/update:179:25

[axic]

@cameel you're correct! Also found that I made another change which would make this "obsolete". It was stuck in a branch for 3 years, made it into a PR #5 now. Do you think we could just merge that?

[cameel]

Switching to an actively mainained package seems like a good idea. It would also probably resolve the issue with axic/keccakjs#13.