Prevent objects from being interpreted as metadata

This will prevent logmessages from being interpreted as metadata.
If a user of winston accidentally inputs a variable pointing to an object as the logmessage,
winston will think the variable is metadata.
ie:
var logMessage = { foo: 'bar' }
log.info(logMessage); // The object of logMessage will be interpreted as metadata and the logmessage will be blank
Console output:
info:  foo=bar

After the patch logMessage will be intepreted as the message
Console output:
info: { foo: 'bar' }
Metadata can still be passed as usual.