Updated version of build-tools to 20 to satisfy new minimum requirement of platform-tools

.travis.yml

@@ -4,7 +4,7 @@ before_install:
   # Install base Android SDK
     - sudo apt-get update -qq
     - sudo apt-get install -qq libstdc++6:i386 lib32z1 expect
-    - export COMPONENTS="build-tools-18.1.0,android-14,android-17,android-19,sysimg-19,extra-android-support"
+    - export COMPONENTS="build-tools-20.0.0,android-14,android-17,android-19,sysimg-19,extra-android-support"
     - export LICENSES="android-sdk-license-5be876d5|android-sdk-license-598b93a6"
     - curl -3L https://raw.github.com/embarkmobile/android-sdk-installer/version-2/android-sdk-installer | bash /dev/stdin --install=$COMPONENTS --accept=$LICENSES
     - source ~/.android-sdk-installer/env