Return a nonzero exit code from nvm_rc_version when no .nvmrc found
If there's no "default" specified, fall back to an .nvmrc file.
Unit tests: add `nvm_has`
Unit tests: add `nvm_find_up`
Use `nvm_normalize_version` in `nvm_version_greater`
Use `nvm_version_greater` in `nvm_binary_available`
Merge pull request #525 from creationix/add_unit_tests

Add unit tests