API27出现Failed to resolve:com.android.support:appcompat-v7:27.+

问题：API27出现Failed to resolve:com.android.support:appcompat-v7:27.+
解决方案：在对应的build.gradle中的buildTypes{}中加入以下repositories代码：

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
        repositories {
            maven {
                url "https://maven.google.com"
            }
        }
    }