travis: Use a stripped bitcoind bundle

I went and stripped all the parts from the bitcoind tarball and uploaded it to
a GCS bucket. Let's see how much we save.

.travis/build.sh

@@ -22,8 +22,8 @@ mkdir -p dependencies/bin || true
 
 # Download bitcoind and bitcoin-cli 
 if [ ! -f dependencies/bin/bitcoind ]; then
-    wget https://bitcoin.org/bin/bitcoin-core-0.18.1/bitcoin-0.18.1-x86_64-linux-gnu.tar.gz
-    tar -xzf bitcoin-0.18.1-x86_64-linux-gnu.tar.gz
+    wget https://storage.googleapis.com/c-lightning-tests/bitcoin-0.18.1-x86_64-linux-gnu.tar.bz2
+    tar -xjf bitcoin-0.18.1-x86_64-linux-gnu.tar.bz2
     mv bitcoin-0.18.1/bin/* dependencies/bin
     rm -rf bitcoin-0.18.1-x86_64-linux-gnu.tar.gz bitcoin-0.18.1
 fi