title: Error: attribute 'package' in <manifest> tag is not a valid Android package name
body: <p>I am trying to write an android app, which used to build once upon a time. Now, everytime I build, I get the following error:</p>
  
  <pre><code>Caused by: com.android.builder.internal.aapt.v2.Aapt2Exception: Android resource linking failed
  C:\Users\Jay\AndroidStudioProjects\DndTools-App\app\build\intermediates\merged_manifests\debug\AndroidManifest.xml:2: AAPT: 
  error: attribute 'package' in &lt;manifest&gt; tag is not a valid Android package name: 'dndtools'.
  </code></pre>
  
  <p>I originally started off with an android-kotlin tutorial as the base, since I wanted to familiarize myself with kotlin and android, if that might be relevant. Also, "Merged Manifest" has <code>package = dndtools</code> instead of <code>com.dndtools.android.dndtools</code> listed, also not sure if relevant.</p>
  
  <p>AndroidManifest.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      package="com.dndtools.android.dndtools"&gt;
  
    &lt;application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name" //dndtools
  ...
  </code></pre>
  
  <p>build.gradle</p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  apply plugin: 'kotlin-android'
  
  apply plugin: 'kotlin-android-extensions'
  def androidSupportVersion = '28.0.0'
  
  android {
      compileSdkVersion 28
      buildToolsVersion "28.0.3"
      defaultConfig {
          applicationId "dndtools"
          minSdkVersion 21
          targetSdkVersion 28
  ...
  </code></pre>
  
  <p>I have searched the internet, and others who had this error usually had an underscore at the start or end of their applicationId (which is not the case here), so I am really at a loss</p>