Fix failure of build script.

Specify version of gradle-rxjava-project-plugin explicitly.

Author: Takeshi SASAKI

.travis.yml

@@ -6,5 +6,6 @@ jdk:
 android:
   components:
     - android-20
+    - build-tools-20.0.0
 
 script: "./gradlew build"

build.gradle

@@ -1,8 +1,8 @@
 buildscript {
   repositories { jcenter() }
   dependencies {
-    classpath 'com.netflix.nebula:gradle-rxjava-project-plugin:1.12.+'
-    classpath 'com.netflix.nebula:gradle-extra-configurations-plugin:1.12.+'
+    classpath 'com.netflix.nebula:gradle-rxjava-project-plugin:1.12.13'
+    classpath 'com.netflix.nebula:gradle-extra-configurations-plugin:1.12.3'
   }
   configurations.classpath.resolutionStrategy {
     // The above dependency will bring in guava, which then pollutes child projects