After update to Android Studio 3.1 I'm facing this error: Could not find org.jetbrains.kotlin:kotlin-stdlib-jre8:1.2.0

JCenter was being cranky the other day, so following should help:

    repositories {
        mavenCentral() // <-- add this at top
        google()
        jcenter()
    }

Add the JCenter repo to your Project-level build.gradle file:

buildscript {
    dependencies {
        repositories {
            //...
            google()
            jcenter() // <--- this is needed
        }

        classpath 'com.android.tools.build:gradle:3.1.0'
    }
}

Working like this

buildscript {
    ext.kotlin_version = '1.1.1'  //Add this line
    repositories {
        jcenter()
        google()
    }
    dependencies {

        classpath 'com.android.tools.build:gradle:3.1.0'
        classpath 'com.google.gms:google-services:3.2.0'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

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