关于Error:Execution failed for task ':app:preDebugAndroidTestBuild'.

新建项目的时候，会碰到默认版本号的问题 > Conflict with dependency 'com.android.support:support-annotations' in project ':app'. Resolved versions for app (26.1.0) and test app (27.1.1) differ. See https://d.android.com/r

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