Support Asciicast v2 format

I always get the same error with the CLI:

SyntaxError: Unexpected token [ in JSON at position 125
    at JSON.parse (<anonymous>)
    at Socket.process.stdin.on.on.once (/Users/felix/src/ps-nvm/vs/v10.8.0/lib/node_modules/asciicast-to-svg/cli.js:44:20)
    at Object.onceWrapper (events.js:273:13)
    at Socket.emit (events.js:187:15)
    at endReadableNT (_stream_readable.js:1081:12)
    at process._tickCallback (internal/process/next_tick.js:63:19)

cast file:

{"version": 2, "width": 160, "height": 40, "timestamp": 1534244114, "env": {"SHELL": "/bin/bash", "TERM": "xterm-256color"}}
[0.010865, "o", "\u001b[?1034hbash-3.2$ "]
[1.861431, "o", "e"]
[1.979978, "o", "c"]
[2.092802, "o", "h"]
[2.244695, "o", "o"]
[2.348721, "o", " "]
[2.445007, "o", "t"]
[2.507652, "o", "e"]
[2.669375, "o", "s"]
[2.805007, "o", "t"]
[3.469918, "o", "\r\n"]
[3.470138, "o", "test\r\nbash-3.2$ "]
[4.58894, "o", "e"]
[4.78088, "o", "x"]
[4.918007, "o", "i"]
[4.964743, "o", "t"]
[5.196836, "o", "\r\n"]
[5.19714, "o", "exit\r\n"]

Command I run:

cat test.cast | asciicast-to-svg 0 > test.svg