Failed to resolve: com.android.support:appcompat-v7:27.+ 报错解决方法

app module build.gradle dependencies中默认配置如下：

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-v7:27.+'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
testCompile 'junit:junit:4.12'
}

Studio 2.3版本应该在Root Project build.gradle allprojects配置如下：

allprojects {
repositories {
jcenter()
maven { url "https://maven.google.com" }
}
}

Studio 3.0版本应该在Root Project build.gradle allprojects配置如下：

allprojects {
repositories {
jcenter()
google()
}
}