Update setup-node-ubuntu.bash to replace `arch` call with portable call to `uname -a`

setup-node-ubuntu.bash

@@ -27,15 +27,15 @@ then
   NODEJS_NAME="iojs"
 fi
 
-if [ -n "$(arch | grep aarch64)" ]; then
+if [ -n "$(uname -a | grep aarch64)" ]; then
   ARCH="arm64"
-elif [ -n "$(arch | grep 64)" ]; then
+elif [ -n "$(uname -a | grep 64)" ]; then
   ARCH="x64"
-elif [ -n "$(arch | grep armv8l)" ]; then
+elif [ -n "$(uname -a | grep armv8l)" ]; then
   ARCH="arm64"
-elif [ -n "$(arch | grep armv7l)" ]; then
+elif [ -n "$(uname -a | grep armv7l)" ]; then
   ARCH="armv7l"
-elif [ -n "$(arch | grep armv6l)" ]; then
+elif [ -n "$(uname -a | grep armv6l)" ]; then
   ARCH="armv6l"
 else
   ARCH="x86"