Adds cwd value to gruntfile's copy:dist

Adds cwd value so grunt copies the files in build/lib/**/* to lib/ instead of lib/build/lib. Unfortunately, running `grunt dist` after this fails with:
```
Running "build:release" (build) task
compiling src/data/env.js
compiling src/data/stringMap.js
compiling src/data/termTree.js
compiling src/data/transforms.js
compiling src/expander.js
Warning: Line 565: Illegal newline after throw
[... else { throw e ; } ...] Use --force to continue.

Aborted due to warnings.
```