How to solve the conflict dependency on RxJava version 1 and 2 : I only used RxJava2 ,but Why occured conflict with RxJava1.1.5

Error:Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.
> com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/rxjava.properties
  	File1: /home/panhao/Android/myGradle/caches/modules-2/files-2.1/io.reactivex.rxjava2/rxjava/2.0.0-RC5/ecd92d1147d9858c23087801a3bc2f323d481472/rxjava-2.0.0-RC5.jar
  	File2: /home/panhao/Android/myGradle/caches/modules-2/files-2.1/io.reactivex/rxjava/1.1.5/ece7b5d0870e66d8226dab6dcf47a2b12afff061/rxjava-1.1.5.jar