Revise "preversion" and "postversion" npm scripts.
Revise "preversion" and "postversion" npm scripts.

- "preversion" now begins with "npm install." Since we're bundling some dependencies in the UMD build, we want to make sure the packages actually installed in node_modules are up to date with the specified dependencies in package.json and package-lock.json.
- "postversion" now explicitly specifies the URL of the GitHub repo. This should make the script work even if some assumptions (like having a Git remote set up or having a local branch tracking the remote "master") aren't satisfied.

ihmeuw/beaut,ihmeuw/ihme-ui,ihmeuw/beaut,ihmeuw/ihme-ui,ihmeuw/beaut,ihmeuw/ihme-ui