Always precompile to a string.

In Handlebars 1.x `false` was the default for `precompile`, but as of
2.0 it is defaulted to `true` (which returns an object literal instead
of the string representation of that object).

This is a backwards compatible change.
Merge pull request #8 from rwjblue/ensure-precompile-to-string

Always precompile to a string.