OneSignal and Gradle error

I dont know where I went wrong, but this keeps me saying

All com.android.support libraries must use the same exact version
specification (mixing versions can lead to runtime crashes.) Found
versions 25.3.1, 24.0.0. Examples include com.android.support:animated
vector-drawable:25.3.1 and com.android.support:customtabs-v7:24.0.0

my build.gradle is

buildscript {
repositories {
    maven { url 'https://maven.fabric.io/public' }

    mavenCentral()
}

dependencies {
    classpath 'io.fabric.tools:gradle:1.22.1'
    classpath 'com.jakewharton.hugo:hugo-plugin:1.2.1'
  }
}
apply plugin: 'com.android.application'
apply plugin: 'io.fabric'
apply plugin: 'com.jakewharton.hugo'

repositories {
    maven { url 'https://maven.fabric.io/public' }
}


android {
  compileSdkVersion 25
  buildToolsVersion '25.0.3'
  defaultConfig {
    applicationId "cosmic.com.fest"
    minSdkVersion 16
    targetSdkVersion 25
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    vectorDrawables.useSupportLibrary = true
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}

flavorDimensions "server"

productFlavors {

    local {
        applicationId "cosmic.com.fest.local"
        dimension 'server'
    }

    dev {
        applicationId "cosmic.com.fest"
        dimension 'server'
    }
  }



defaultConfig {
    manifestPlaceholders = [onesignal_app_id: "something",
    onesignal_google_project_number: "something"]
  }
}

def ANDROID_SUPPORT_VERSION = "25.3.1"

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.crashlytics.sdk.android:crashlytics:2.6.8@aar') {
    transitive = true;
}
compile "com.android.support:appcompat-v7:$ANDROID_SUPPORT_VERSION"
compile 'com.android.support.constraint:constraint-layout:1.0.2'
compile 'com.afollestad.material-dialogs:core:0.8.6.1'
compile 'com.orhanobut:logger:1.15'
compile 'com.squareup.retrofit2:retrofit:2.3.0'
compile 'com.squareup.retrofit2:converter-gson:2.0.2'
compile "com.android.support:design:$ANDROID_SUPPORT_VERSION"
compile "com.android.support:support-vector-drawable:$ANDROID_SUPPORT_VERSION"
testCompile 'junit:junit:4.12'
compile 'org.apache.commons:commons-lang3:3.5'
compile "com.android.support:recyclerview-v7:$ANDROID_SUPPORT_VERSION"

compile 'com.google.firebase:firebase-messaging:10.2.6'

compile 'com.onesignal:OneSignal:3.5.6'

// Required for OneSignal, even if you have added FCM.
compile 'com.google.android.gms:play-services-gcm:10.2.6'

// Required for geotagging
compile "com.google.android.gms:play-services-location:10.2.6"

// play-services-analytics is only needed when using 8.1.0 or older.
compile 'com.google.android.gms:play-services-analytics:10.2.6'
}

I need to add OneSignal notifications with Firebase to obtain tokens.

When I tried this solution, my appcompat would still complain the same.