move node-mbgl to platform/node/ directory

platform/node/scripts/install_node.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+set -e
+set -o pipefail
+
+# Mason exists on PATH from sourcing mbgl install script
+mapbox_time $NODE_EXE \
+mason install $NODE_EXE $NODE_VERSION
+
+export PATH="`mason prefix $NODE_EXE $NODE_VERSION`/bin":"$PATH"
+
+$NODE_EXE --version
+npm --version