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

Error:Execution failed for task ':app:preDebugAndroidTestBuild'.
 
> 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/tools/test-apk-dependency-conflicts.html for details.

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:26.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.2'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}

build.gradle 내의 dependencies 블록 내용을 아래와 같이 수정 한다.

'com.android.support.test:runner:1.0.1'

'com.android.support.test.espresso:espresso-core:3.0.1'