Add 'enact' install script to ensure node_sass module gets installed

Node-sass-middleware has a dependency module, node-sass, which
needs to get installed first. Unfortunately, for some reason,
the current version of node-sass does not properly run
its install script to download the binary file it needs to
operate. See sass/node-sass#1579
for more details.

To fix this, we hadd an 'enact' script to elasticbeanstalk
configuration, to tell it to run the node-sass installer
manually during deployment. This ensures that the binary
file gets installed.

.ebextensions/node_sass_install.config

@@ -0,0 +1,13 @@
+commands:
+  create_enact_dir:
+    command: "mkdir /opt/elasticbeanstalk/hooks/appdeploy/enact"
+    ignoreErrors: true
+files:
+  "/opt/elasticbeanstalk/hooks/appdeploy/enact/node_sass_install.sh":
+    mode: "000755"
+    owner: root
+    group: root
+    content: |
+      #!/usr/bin/env bash
+      . /opt/elasticbeanstalk/support/envvars
+      node /var/app/current/node_modules/node-sass-middleware/node_modules/node-sass/scripts/install.js