[fix] catch exceptions for file transport unlinkSync

[calvinfo]

Using cluster, I sometimes run more than one winston logger on a
single instance. Occasionally they both detect that they should
remove the log file, and one will unlink before the other. This
adds a try...catch to make sure that the unlinkSync call doesn't
throw.

I'd be happy to modify the PR to provide some way of notifying the
developer that the unlink failed. I didn't see a good one off the bat,
ordinarily I'd use something like debug().

[diversario]

I have the same issue. Workaround, I suppose, it to have a separate file for each logger instance, but that gets messy.

[indexzero]

This looks good. Will go into the next version of winston@0.8.x

[indexzero]

Cherry-picked. Thanks!

[shaharke]

This still happens in winston 0.9.0.

[shaharke]

Here's the stack trace:

fs.js:765
return binding.unlink(pathModule._makeLong(path));
^
Error: ENOENT, no such file or directory '/var/log/bigpanda/intelligence.log'
at Object.fs.unlinkSync (fs.js:765:18)
at File._getFile (/opt/bigpanda/intelligence/node_modules/bp-api-common/node_modules/winston/lib/winston/transports/file.js:557:12)
at /opt/bigpanda/intelligence/node_modules/bp-api-common/node_modules/winston/lib/winston/transports/file.js:529:31
at Object.oncomplete (fs.js:107:15)

And the relevant lines:
https://github.com/winstonjs/winston/blob/v0.9.0/lib/winston/transports/file.js#L557-L557