Fix flakiness with Gulp + Travis

Gulp was failing silently on Travis. I tracked this down to the task that
builds a custom, slimmed-down version of jQuery from source.

To fix this I’ve removed the task and replaced it with just `src`ing the
minified version of jQuery from `node_modules`.

Cons:
- A few more kb of JS

Pros:
- Less random, afternoon-chewing complexity

README.md

@@ -33,13 +33,14 @@ n is a tool for managing different versions of node. The following installs n an
     npm install -g n
     n latest
     npm rebuild node-sass
- 
+
 Most of the frontend dependencies are managed using Git Submodules. Some are
 managed with NPM and Bower. To install or update *all the things*, run
 ```shell
-    git submodule init 
+    git submodule init
     git submodule update
     npm install
+    npm run build
 ```
 
 If you want the front end assets to re-compile on changes, leave this running