android: update build and target SDK versions

Note that Android 9 Pie (API 28) disallows HTTP requests by default, so an
exception was needed in the app in order for the Metro bundler to work in debug
mode.

android/app/src/main/AndroidManifest.xml

       android:icon="@mipmap/ic_launcher"
       android:label="@string/app_name"
       android:name=".MainApplication"
+      android:networkSecurityConfig="@xml/network_security_config"
       android:theme="@style/AppTheme">
     <activity
         android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|screenSize|smallestScreenSize"

android/app/src/main/res/xml/network_security_config.xml

+<network-security-config>
+    <domain-config cleartextTrafficPermitted="true">
+        <domain includeSubdomains="true">localhost</domain>
+    </domain-config>
+</network-security-config>

android/build.gradle

         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.1.4'
+        classpath 'com.android.tools.build:gradle:3.2.1'
         classpath 'com.google.gms:google-services:3.2.1'
 
         // NOTE: Do not place your application dependencies here; they belong
 }
 
 ext {
-    buildToolsVersion = "27.0.3"
-    compileSdkVersion = 27
+    buildToolsVersion = "28.0.3"
+    compileSdkVersion = 28
     minSdkVersion    = 21
-    targetSdkVersion = 26
-    supportLibVersion = "27.1.1"
+    targetSdkVersion = 28
+    supportLibVersion = "28.0.0"
 
     // The Maven artifact groupdId of the third-party react-native modules which
     // Jitsi Meet SDK for Android depends on and which are not available in

android/gradle/wrapper/gradle-wrapper.properties

-#Fri Sep 08 10:42:14 CEST 2017
+#Wed Dec 19 12:02:47 CET 2018
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.7-all.zip