disable pre-dexing for CI builds

.travis.yml

@@ -27,6 +27,7 @@ jdk:
   - oraclejdk8
 
 env:
+  - TRAVIS_BUILD=true
   global:
     MALLOC_ARENA_MAX=2
 

build.gradle

@@ -53,6 +53,13 @@ subprojects {
                     exclude 'META-INF/ASL2.0'
                 }
 
+                if (System.getenv('TRAVIS_BUILD') == 'true') {
+                    System.out.println("Is travis build, disable pre-dexing")
+                    dexOptions {
+                        preDexLibraries = false;
+                    }
+                }
+
                 if (android.hasProperty('buildTypes') && project.plugins.hasPlugin('com.android.application')) {
                     android.buildTypes.each { buildType ->
                         File file = rootProject.file('signing.properties')