Updating gradle and build tools version

Change-Id: I269788d6d7798a5324a9170935c31a7c565cc214
diff --git a/build.gradle b/build.gradle
index 51ac5a1..9c71693 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,9 +1,10 @@
 buildscript {
     repositories {
         mavenCentral()
+        jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.3'
+        classpath 'com.android.tools.build:gradle:2.3.1'
         classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.0'
     }
 }
@@ -13,7 +14,7 @@
 
 android {
     compileSdkVersion 26
-    buildToolsVersion '24.0.0'
+    buildToolsVersion '26.0.0'
 
     defaultConfig {
         minSdkVersion 21
@@ -61,6 +62,7 @@
 
 repositories {
     mavenCentral()
+    jcenter()
 }
 
 final String SUPPORT_LIBS_VERSION = '26.0.0-SNAPSHOT'