Use environment variable for Socket Firewall npm token (#440)

Author: DecIntercom

.npmrc

@@ -1,4 +1,4 @@
 registry = https://socket-firewall-registry.corporate.intercom.io/npm
-//socket-firewall-registry.corporate.intercom.io/npm/:_authToken = "BYUi5HGeKW4GPN1z6PXqjeo3IVmLJ9uFA8TQFzoP2VbRt3h0J9AMaqz9A"
+//socket-firewall-registry.corporate.intercom.io/npm/:_authToken = ${SOCKET_FIREWALL_NPM_TOKEN}
 strict-ssl = true
 always-auth = true