bump android target version to 27 (facebook#20843)

Summary:
bump target version to 27
pass all current ci.
none
[GENERAL] [ANDROID] [FEATURE] - bump android target version to 27
Pull Request resolved: facebook#20843

Differential Revision: D9845999

Pulled By: hramos

fbshipit-source-id: 3c532a2d5a2b7d201bacab54cf3d60e1efffb653

Author: gengjiawen

RNTester/android/app/build.gradle

@@ -90,7 +90,7 @@ android {
     defaultConfig {
         applicationId "com.facebook.react.uiapp"
         minSdkVersion 16
-        targetSdkVersion 26
+        targetSdkVersion 27
         versionCode 1
         versionName "1.0"
         ndk {

ReactAndroid/build.gradle

@@ -251,7 +251,7 @@ android {
 
     defaultConfig {
         minSdkVersion 16
-        targetSdkVersion 26
+        targetSdkVersion 27
         versionCode 1
         versionName "1.0"
 

local-cli/templates/HelloWorld/android/build.gradle

@@ -5,7 +5,7 @@ buildscript {
         buildToolsVersion = "27.0.3"
         minSdkVersion = 16
         compileSdkVersion = 27
-        targetSdkVersion = 26
+        targetSdkVersion = 27
         supportLibVersion = "27.1.1"
     }
     repositories {