chore: move tsd to a devDependency for faster npm install times.

[mprobst]

Fixes #159.

[alexeagle]

I see Igor's comment about this, but I having it as a devDependency broke angular.
#138
which I fixed by moving from devDependency to regular dependency.

I think our only fix here is to write a release script rather than rely on npm to perform the right things in the right order.

[mprobst]

@alexeagle yeah, but that was when we ran tsd reinstall in npm install as a preinstall script, right? Now that we only run it on publish, we should be fine.