Could not find manifest-merger.jar (com.android.tools.build:manifest-merger:26.0.1)

I finally fixed the issue. This may be a workaround but it works. So if anyone having this issue, just follow this:

1. Swap the position of jcenter() and google() in project gradle file and in also all the other module you have in your project. Like in mine I have crashlytics, fabric so just remember to make the changes in their build.gradle file as well:

   buildscript {
       repositories {
           jcenter()
           google()
       }
   }
   

   to

   buildscript {
       repositories {
           google()
           jcenter()
       }
   }
   

2. Before building your project again go to your project folder and delete the .gradle folder from your project and then build your project.

1. Go to Publishing Settings/Build, enable Custom Gradle Template
2. Go to Assets/Plugins/Android/mainTemplate.gradle and change the postion from

  buildscript {
    repositories {
        jcenter()
        google()
}

to

 buildscript {
   repositories {
      google()
      jcenter()
}

3. Remove gradle cache and rebuild. For Mac you can run rm -rf $HOME/.gradle/caches/ in terminal.