Closure's base path terminator check fails on Windows

In `node_modules/closure.js` the path `goog_.CLOSURE_BASE_PATH` is required to end with a `/` character.
Using `path.join` to compute the base path in `lib/index.js` causes the path to end with a `\` on Windows. Replacing `path.join` with concatenation solves the problem.

Tests pass on Windows 7 64-bit, Node 0.8.14