dependency "tmp" should be updated

[mojoaxel]

"dependencies": {
    "tmp": "0.0.23"
}

"tmp" is quite old and produces a warning in node >6:

(node:4526) DeprecationWarning: os.tmpDir() is deprecated. Use os.tmpdir() instead.

[epexa]

I also got an error in Node 7.0.0:

DeprecationWarning: os.tmpDir() is deprecated. Use os.tmpdir() instead.

Variable in file image-diff\node_modules\tmp\lib\tmp.js in 17 line: tmpDir = os.tmpDir || _getTMPDir,