update to latest build tools and gradle

- add new flavordimension tag

app/build.gradle

@@ -2,7 +2,7 @@ apply plugin: 'com.android.application'
 
 android {
     compileSdkVersion 25
-    buildToolsVersion "25"
+    buildToolsVersion '26.0.2'
     defaultConfig {
         applicationId "org.torproject.android"
         minSdkVersion 16
@@ -20,8 +20,12 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
         }
     }
+
+    flavorDimensions "free"
+
     productFlavors {
         minimalperm {
+            dimension "free"
             minSdkVersion 16
             applicationId 'org.torproject.android'
             targetSdkVersion 23
@@ -30,6 +34,7 @@ android {
             versionName '15.5.0-RC-1-multi-SDK16'
         }
         fullperm {
+            dimension "free"
             minSdkVersion 23
             applicationId 'org.torproject.android'
             targetSdkVersion 25

build.gradle

@@ -4,7 +4,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.3'
+        classpath 'com.android.tools.build:gradle:3.0.0'
     }
 }
 

gradle/wrapper/gradle-wrapper.properties

-#Sun Mar 19 08:31:31 EDT 2017
+#Tue Oct 31 09:37:18 EDT 2017
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-3.3-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip

jsocksAndroid/build.gradle

@@ -2,7 +2,7 @@ apply plugin: 'com.android.library'
 
 android {
     compileSdkVersion 25
-    buildToolsVersion "25"
+    buildToolsVersion '26.0.2'
 
     defaultConfig {
         minSdkVersion 8

orbotservice/build.gradle

@@ -2,7 +2,7 @@ apply plugin: 'com.android.library'
 
 android {
     compileSdkVersion 25
-    buildToolsVersion "25"
+    buildToolsVersion '26.0.2'
 
     sourceSets {
         main {