"No such file or directory" error if pptip run outside of the the package root

[mshenfield]

If pptip is run outside of the project root, an error is thrown. It looks like it is resolving ./pragmaticprogrammer.txt to the current working directory. I think using __dirname might fix it - testing locally. Expect a PR!

node: 4.2.1
pp-daily-tip: 1.0.0

Error:

fs.js:549
  return binding.open(pathModule._makeLong(path), stringToFlags(flags), mode);
                 ^

Error: ENOENT: no such file or directory, open './pragmaticprogrammer.txt'
    at Error (native)
    at Object.fs.openSync (fs.js:549:18)
    at Object.fs.readFileSync (fs.js:397:15)
    at Object.<anonymous> (/path/to/gitcheckout/of/daily-pragmatic-tip/index.js:5:15)
    at Module._compile (module.js:435:26)
    at Object.Module._extensions..js (module.js:442:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:311:12)
    at Function.Module.runMain (module.js:467:10)
    at startup (node.js:134:18)