android studio build apk作成

apkを作成しようと思い、buildを行おうとしたら以下のようなエラーが出ました、
どのようなことが考えられるのでしょうか？

Error:Execution failed r task ':app:transformClassesWithDexForDebug'.
> com.android.build.api.transform.TransformException: com.android.ide.common.process.ProcessException: java.util.concurrent.ExecutionException: com.android.dex.DexException: Multiple dex files define Lorg/java_websocket/WebSocketListener;

build.gradleは以下になります

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "24.0.0"
    defaultConfig {
        applicationId "com.example.owner.login"
        minSdkVersion 21
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:23.4.0'
    testCompile 'junit:junit:4.12'
    compile ('io.socket:socket.io-client:0.8.1') {
        exclude group: 'org.json', module: 'json'
    }

    compile fileTree(dir: 'libs', include: ['json-20160810.jar'])
}

repositories{
    flatDir{
        dirs 'libs'
    }
}