Upgrade to express 4.x and add devDependency

Review URL: https://github.com/google/traceur-compiler/pull/1150

Closes #1150.
Remove ObjectMap and ArrayMap and use std Map instead
Lock dependencies to minor-version, track patch version
Lock major-version, track minor-version
Sync up to source-map 0.1.34.
Improve source map accuracy.
respond to review