fix install_node [publish binary]

scripts/install_node.sh

@@ -1,9 +1,21 @@
+#!/usr/bin/env bash
+
+if [[ ${1:-false} == 'false' ]]; then
+    echo "Error: pass node version as first argument"
+    exit 1
+fi
+
+NODE_VERSION=$1
+
+# if an existing nvm is already installed we need to unload it
+nvm unload || true
+
 # here we set up the node version on the fly based on the matrix value.
 # This is done manually so that the build works the same on OS X
-rm -rf ~/.nvm/ && git clone --depth 1 https://github.com/creationix/nvm.git ~/.nvm
-source ~/.nvm/nvm.sh
-nvm install $1
-nvm use $1
+rm -rf ./__nvm/ && git clone --depth 1 https://github.com/creationix/nvm.git ./__nvm
+source ./__nvm/nvm.sh
+nvm install ${NODE_VERSION}
+nvm use ${NODE_VERSION}
 node --version
 npm --version
-which node
+which node