implementation ‘com.android.support:appcompat-v7:27.1.1’ [on hold]

i am trying to connect my app with firebase.i follow all the procedure accordingly still i am having this problem from last 2 hours.

my app performance stuck here.its just loading from last 2 hours

dependencies {     implementation fileTree(dir: 'libs', include: ['*.jar'])     implementation 'com.android.support:appcompat-v7:27.1.1'     implementation 'com.android.support.constraint:constraint-layout:1.1.3'     testImplementation 'junit:junit:4.12'     androidTestImplementation 'com.android.support.test:runner:1.0.2'     androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'     implementation 'com.google.firebase:firebase-core:16.0.1' } apply plugin: 'com.google.gms.google-services' 

I watch different video and dependencies changed but still problem is not solved.

this line of code continuously showing Red underline