Force package.json and package-lock.json to end in LF

[brettcannon]

As reported in npm/npm#17161, npm rewrites both package.json and package-lock.json to have LF line endings. That sucks when you have autocrlf=auto turned on for git.

Basically we need to add a .gitattributes file with the following to make it so running npm on Windows doesn't constantly leading to git thinking there are file changes to commit:

package.json text eol=lf
package-lock.json text eol=lf