Upgrade dependencies to latest versions

As reported by the gradle-versions-plugin.

Change-Id: I2a9bda3464c82b37cbc7af89dbfb4425213a08e1
diff --git a/app/build.gradle b/app/build.gradle
index 2f5b98c..c080d63 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -23,9 +23,9 @@
     compile fileTree(include: ['*.jar'], dir: 'libs')
     testCompile 'junit:junit:4.12'
     compile files('libs/gerrit-rest-java-client-0.8.8-SNAPSHOT.jar')
-    compile 'com.google.guava:guava:19.0-rc2'
+    compile 'com.google.guava:guava:19.0'
     compile 'org.apache.httpcomponents:httpclient-android:4.3.5.1'
-    compile 'com.google.code.gson:gson:2.3.1'
+    compile 'com.google.code.gson:gson:2.6.2'
     compile 'com.android.support:appcompat-v7:23.1.1'
     compile 'com.android.support:design:23.1.1'
     compile 'com.android.support:support-v4:23.1.1'