Added minimum sdk requirement on AndroidManifest

Author: lidongze91

android/src/main/AndroidManifest.xml

@@ -1,12 +1,13 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           xmlns:tools="http://schemas.android.com/tools"
           package="com.flutter_webview_plugin">
+    <uses-sdk android:minSdkVersion="16" />
     <application>
         <provider
             android:name="androidx.core.content.FileProvider"
             android:authorities="${applicationId}.fileprovider"
             android:exported="false"
-            android:grantUriPermissions="true" 
+            android:grantUriPermissions="true"
             tools:replace="android:authorities">
             <meta-data
                 android:name="android.support.FILE_PROVIDER_PATHS"