Cleanup passes Typescript and Travis are incompatible

[TimvdLippe]

The Travis pass overrides the install script (https://github.com/PolymerLabs/tedium/blob/3684899d7ca344e84f4a1d7098ad794b36fe6ae4/cleanup-passes/travis.ts#L71-L76), but the TypeScript pass actually introduces npm dependencies to be able to generate the TypeScript definitions.

To this end, when you run both Travis and TypeScript, the command npm install (which is the default Travis install command) is no longer run, thus the npm dependencies for gen-typescript-declarations are no longer installed.

Instead, the current commands in install should be moved to the first lines of before_script, such that install once again runs npm install on Travis.