Fix UnsupportedOperationException bug

[xuwei-k]

このtree

ef10b40

の状態でtestすると以下のようなエラーがでます

[info] - test normal 1 *** FAILED ***                                                                     
[info]   java.lang.UnsupportedOperationException:                                                         
[info]   at java.util.AbstractMap.put(AbstractMap.java:186)                                               
[info]   at org.fluentd.logger.scala.FluentLogger.log(FluentLogger.scala:17)                              
[info]   at org.fluentd.logger.scala.FluentLogger.log(FluentLogger.scala:12)                              
[info]   at org.fluentd.logger.scala.FluentLoggerSuite$$anonfun$1.apply$mcV$sp(FluentLoggerSuite.scala:46)
[info]   at org.fluentd.logger.scala.FluentLoggerSuite$$anonfun$1.apply(FluentLoggerSuite.scala:32)       
[info]   at org.fluentd.logger.scala.FluentLoggerSuite$$anonfun$1.apply(FluentLoggerSuite.scala:32)       
[info]   at org.scalatest.FunSuite$$anon$1.apply(FunSuite.scala:1265)                                     
[info]   at org.scalatest.Suite$class.withFixture(Suite.scala:1974)                                       
[info]   at org.fluentd.logger.scala.FluentLoggerSuite.withFixture(FluentLoggerSuite.scala:29)            
[info]   at org.scalatest.FunSuite$class.invokeWithFixture$1(FunSuite.scala:1262)                         

ここ

https://github.com/oza/fluent-logger-scala/blob/4915e4e34e1a94af92623db24c7cf27c26a4297a/src/main/scala/org/fluentd/logger/scala/FluentLogger.scala#L16-L18

で、まず scala の immutable な Map に対して put を呼ぶ => つまり java.util.Map に暗黙変換して、そのメソッドを呼んでますが、 scalaのimmutableな Map から java.util.Map に暗黙変換しても、型がjava.util.Map になっただけで実態はimmutableなので、これでは 必ず UnsupportedOperationException がでます。

[oza]

Thanks for your pull request! I got it and merged it.