Set externals properly for UMD builds

[patrickarlt]

Close #128.

@tomwayson @jgravois I did verify that this makes bundles smaller but you should verify that the demos still work. I probably inadvertently removed this while setting up the build system.

[coveralls]

Coverage remained the same at 100.0% when pulling 2f77c9f on proper-externals into 22f84e2 on master.

[tomwayson]

Demos that I've tested so far:

• gecode-browser
• ago-node-cli

I think if we test one of the auth ones we can merge. I have to run, but will try that later.

[jgravois]

I think if we test one of the auth ones we can merge.

our only real auth demo uses Express (and consequently doesn't load UMDs, much like ago-node-cli). that said, my own browser geocoding demo has its own OAuth implementation for batch geocoding. i confirmed locally that (a) the UMDs did indeed shrink and (b) didn't bust anything auth related.

all said, nice catch @tomwayson and truly elegant fix @patrickarlt. i was stuck on the idea that we'd need to omit the package we actually wanted to bundle from the externals: [].

thinking about it more, your one liner makes sense because internally a package wouldn't include an import that referenced its own name.

[tomwayson]

duh - forgot this repo did it's own CJS builds. so glad I tested ago-node-cli! thanks @jgravois