Merge pull request 'Fix env var name for assets' (#1) from kris/fix_asset_env_var into master

Reviewed-on: https://git.bubblev.org/bubblev/bubble-web/pulls/1

README.md

@@ -16,7 +16,7 @@ Build it:
 
 In your `${HOME}/.bubble-test.env` file, add this line (fix the path to point to the correct location of your `bubble-web/dist` directory):
 
-    export ASSETS_DIR=/path/to/bubble-web/dist
+    export BUBBLE_ASSETS_DIR=/path/to/bubble-web/dist
 
 In the `bubble/bubble-server` directory, run the test named `bubble.test.dev.DevServerTest`, like so: