问gradle发现版本错误

EN

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "com.social.uk"
        minSdkVersion 15
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    androidTestImplementation('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    implementation 'com.android.support:appcompat-v7:27.1.1' // error here
    implementation 'com.android.volley:volley:1.0.0'
    testImplementation 'junit:junit:4.12'
    implementation 'com.android.support:recyclerview-v7:27.1.1'
    implementation 'com.android.support:cardview-v7:27.1.1'
    //compile 'com.google.android.gms:play-services-appindexing:9.8.0'
    implementation 'com.android.support:design:27.1.1'
    implementation 'com.squareup.picasso:picasso:2.5.2'
    implementation 'com.squareup.okhttp3:okhttp:3.7.0'
    implementation 'de.hdodenhof:circleimageview:2.1.0'
    implementation 'com.google.android.gms:play-services-ads:15.0.1'
    implementation 'com.anjlab.android.iab.v3:library:1.0.+'
}