You need to run "nvm install N/A" to install it before using it.
# See the versions you installed
$ nvm ls
v7.5.0
v7.8.0
v8.4.0
default -> v8.1.2 (-> N/A)
node -> stable (-> v8.4.0) (default)
stable -> 8.4 (-> v8.4.0) (default)
# Change the default to correct version of node:
$ nvm alias default v8.4.0
# So, solution is: You need to set a correct default version
# must the one you installed
# for example,set the newest version as default:
$ nvm alias default node