Try using only one connection for NDK download.

.travis.yml

@@ -33,7 +33,7 @@ before_install:
   - sudo apt-get update -qq
   - sudo apt-get install aria2 pv -qq
   - download_extract() { aria2c -x 16 $1 -o $2 && tar -xf $2; }
-  - download_extract_xz() { aria2c -x 16 $1 -o $2 && pv $2 | xz -vd | tar -x; }
+  - download_extract_xz() { aria2c $1 -o $2 && pv $2 | xz -vd | tar -x; }
 # Travis uses CMake 2.8.7. We require 2.8.8. Grab latest
   - if [ "$CMAKE" == "TRUE" ]; then
       sudo apt-get install lib32stdc++6 lib32z1 lib32z1-dev -qq &&