[Fix] ensure LTS alias dir exists before writing to it.
[Fix] ensure LTS alias dir exists before writing to it.

Fixes #1216
creationix/nvm,creationix/nvm,PeterDaveHello/nvm,evocateur/nvm,ljharb/nvm,ljharb/nvm,evocateur/nvm,lukechilds/nvm,PeterDaveHelloKitchen/nvm,edwmurph/nvm,PeterDaveHelloKitchen/nvm,lukechilds/nvm,PeterDaveHello/nvm,edwmurph/nvm