android: Update Gradle plugin and wrapper

src/frontends/android/app/build.gradle

@@ -2,7 +2,7 @@ apply plugin: 'com.android.application'
 
 android {
     compileSdkVersion 23
-    buildToolsVersion "23.0.3"
+    buildToolsVersion '25.0.0'
 
     defaultConfig {
         applicationId "org.strongswan.android"

src/frontends/android/build.gradle

@@ -3,7 +3,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.3'
+        classpath 'com.android.tools.build:gradle:2.3.3'
     }
 }
 

src/frontends/android/gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
-#Tue Sep 20 17:56:35 CEST 2016
+#Tue Apr 18 15:57:06 CEST 2017
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.14.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-3.3-all.zip