title: Androidx Camera: Manifest merger failed : uses-sdk:minSdkVersion 16 cannot be smaller than version 21
body: <p>Hi I am using CameraX api to build custom camera, after adding updated library dependency to build.gradle file, i am getting following build error  </p>
  
  <hr>
  
  <blockquote>
    <p>Manifest merger failed : uses-sdk:minSdkVersion 16 cannot be smaller than version 21 declared in library [androidx.camera:camera-extensions:1.0.0-alpha08] /Users/.gradle/caches/transforms-2/files-2.1/f20dc98c605a4c4dbd6030601f9665d3/camera-extensions-1.0.0-alpha08/AndroidManifest.xml as the library might be using APIs not available in 16
        Suggestion: use a compatible library with a minSdk of at most 16,
            or increase this project's minSdk version to at least 21,
            or use tools:overrideLibrary="androidx.camera.extensions" to force usage (may lead to runtime failures)</p>
  </blockquote>
  
  <hr>
  
  <p>build.gradle file</p>
  
  <pre><code>apply plugin: 'com.android.application'
  apply plugin: 'kotlin-android'
  apply plugin: 'kotlin-android-extensions'
  apply plugin: 'kotlin-kapt'
  
  android {
          compileSdkVersion 29
          buildToolsVersion "29.0.3"
  
          defaultConfig {
                      applicationId ""
                      minSdkVersion 16
                      targetSdkVersion 29
                      versionCode 1
                      versionName "1.0"
                      multiDexEnabled true
                      testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
                      vectorDrawables.useSupportLibrary = true
              }
  
              buildTypes {
                      release {
                          minifyEnabled false
                          proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
                      }
              }
  
              compileOptions {
                      sourceCompatibility JavaVersion.VERSION_1_8
                      targetCompatibility JavaVersion.VERSION_1_8
              }
  
              dataBinding {
                      enabled = true
              }
  
              flavorDimensions 'dimensions'
  
              productFlavors {
  
                      dev {
                          //assembleDevDebug crashlyticsUploadDistributionDevDebug
                          applicationId ""
                          versionName "D(0.0)"   //for QA Release
                          versionCode 00
                          proguardFile("proguard-rules.pro")
                      }
  
                      prod {
                          applicationId ""
                          versionName "1.3" //for prod release
                          versionCode 13
                          proguardFile("proguard-rules.pro")
                          resValue "string", "app_name", "Prod Android"
                      }
              }
  
      }
  
  dependencies {
          implementation fileTree(dir: 'libs', include: ['*.jar'])
          implementation "androidx.camera:camera-core:1.0.0-beta01"
          implementation "androidx.camera:camera-camera2:1.0.0-beta01"
          implementation "androidx.camera:camera-extensions:1.0.0-alpha08"
  
  }
  apply plugin: 'com.google.gms.google-services'
  </code></pre>