I am getting the error,
Error:(11, 0) Plugin with id \'io.fabric\' not found
when trying to run crashlytics on my project.
You just forget to add below mentioned line in Project level gradle file.
maven { url 'https://maven.fabric.io/public' }
Also please add below mentioned line in dependencies (in project level gradle file)
classpath 'io.fabric.tools:gradle:1.26.1'