Fix NDK download in Travis

Summary:
After about 500MB, Travis seems to kill the TLS connection. Could be a traffic
limit, could be a timeout. I've only seen this for their MacOS boxes. We're now
retrying a few times with curl, which seems to work.

Reviewed By: emilsjolander

Differential Revision: D6051024

fbshipit-source-id: feb73bfb9fd81b2a8b9b4d33d4e9f230a9899a66

.travis.yml

@@ -76,7 +76,7 @@ before_install:
       source scripts/android-setup.sh && installAndroidSDK
       export ANDROID_SDK=$ANDROID_HOME
       export ANDROID_NDK_REPOSITORY=$HOME/android-ndk
-      export ANDROID_NDK_HOME=$ANDROID_NDK_REPOSITORY/android-ndk-r13b
+      export ANDROID_NDK_HOME=$ANDROID_NDK_REPOSITORY/android-ndk-r15c
     fi
 
   # JavaScript

scripts/android-setup.sh

@@ -1,8 +1,9 @@
 function download() {
+  echo "Downloading '$1' to '$2' ..."
   if hash curl 2>/dev/null; then
-    curl -L -o $2 $1
+    curl --retry 10 -L -o "$2" "$1"
   elif hash wget 2>/dev/null; then
-    wget -O $2 $1
+    wget -O "$2" "$1"
   else
     echo >&2 "No supported download tool installed. Please get either wget or curl."
     exit