implement utc support for date substitution in filename

Resolves #231

README.md

@@ -27,6 +27,7 @@ The DailyRotateFile transport can rotate files by minute, hour, day, month, year
 * **maxFiles:** Maximum number of logs to keep. If not set, no logs will be removed. This can be a number of files or number of days. If using days, add 'd' as the suffix. (default: null)
 * **options:** An object resembling https://nodejs.org/api/fs.html#fs_fs_createwritestream_path_options indicating additional options that should be passed to the file stream. (default: `{ flags: 'a' }`)
 * **auditFile**: A string representing the name of the name of the audit file. This can be used to override the default filename which is generated by computing a hash of the options object. (default: '.<optionsHash>.json')
+* **utc**: Use UTC time for date in filename. (default: false)
 
 ## Usage
 ``` js

daily-rotate-file.js

@@ -86,7 +86,8 @@ var DailyRotateFile = function (options) {
             max_logs: options.maxFiles,
             end_stream: true,
             audit_file: options.auditFile ? options.auditFile : path.join(self.dirname, '.' + hash(options) + '-audit.json'),
-            file_options: options.options ? options.options : {flags: 'a'}
+            file_options: options.options ? options.options : {flags: 'a'},
+            utc: options.utc ? options.utc : false
         });
 
         this.logStream.on('new', function (newFile) {

test/transport-tests.js

@@ -99,13 +99,14 @@ describe('winston/transports/daily-rotate-file', function () {
 
     describe('when using a filename or dirname', function () {
         var logDir = path.join(__dirname, 'logs');
-        var now = moment().format('YYYY-MM-DD-HH');
+        var now = moment().utc().format('YYYY-MM-DD-HH');
         var filename = path.join(logDir, 'application-' + now + '.log');
         var options = {
             json: true,
             dirname: logDir,
             filename: 'application-%DATE%.log',
-            datePattern: 'YYYY-MM-DD-HH'
+            datePattern: 'YYYY-MM-DD-HH',
+            utc: true
         };
 
         beforeEach(function (done) {