Failure on really large coverage.json files

[dwabyick]

I used this on a really large coverage file, and I ran into a failure:

undefined:2476
          "source": " * Dissemina
                                 ^
SyntaxError: Unexpected end of input
    at Object.parse (native)
    at Object.<anonymous> (/usr/local/lib/node_modules/json2htmlcov/bin/json2htmlcov:21:16)

This appears to be related to limitations in the way that fs.readFileSync('/dev/stdin') is not guaranteed to read in the whole file.
https://github.com/yiwang/json2htmlcov/blob/master/bin/json2htmlcov#L21

Information on this issue is discussed here:
nodejs/node-v0.x-archive#7412

I'll try to submit a pull to fix this issue.