Update Android SDK build-tools to 26.0.3.

An upcoming change will make Bazel only compatible with build-tools
26.0.1 and later. Keep installing 24.0.3 incase we need to rollback that
change.

Change-Id: Ieeb56a5bb510008312a054bbf76e77540a06eda0
diff --git a/gce/linux-android.sh b/gce/linux-android.sh
index df2e8b5..4d3e913 100644
--- a/gce/linux-android.sh
+++ b/gce/linux-android.sh
@@ -38,5 +38,7 @@
     eof
 }
 '
-tools/bin/sdkmanager "platforms;android-24" "platform-tools" "build-tools;24.0.3" "add-ons;addon-google_apis-google-24" "extras;android;m2repository"
+tools/bin/sdkmanager "platforms;android-24" "platform-tools" \
+  "build-tools;24.0.3" "build-tools;26.0.1" \
+  "add-ons;addon-google_apis-google-24" "extras;android;m2repository"
 chown -R ci /home/ci/android
diff --git a/mac/mac-android.sh b/mac/mac-android.sh
index f54b2f4..923cf1b 100644
--- a/mac/mac-android.sh
+++ b/mac/mac-android.sh
@@ -43,4 +43,6 @@
     eof
 }
 '
-tools/bin/sdkmanager "platforms;android-24" "platform-tools" "build-tools;24.0.3" "add-ons;addon-google_apis-google-24" "extras;android;m2repository"
+tools/bin/sdkmanager "platforms;android-24" "platform-tools" \
+  "build-tools;24.0.3;" "build-tools;26.0.1" \
+  "add-ons;addon-google_apis-google-24" "extras;android;m2repository"