only assume ~/.nvm is a git repo if we clone it

scripts/node/install.sh

@@ -15,12 +15,12 @@ fi
 
 if [ ! -d ~/.nvm ]; then
     git clone https://github.com/creationix/nvm.git ~/.nvm
-fi
 
-pushd ~/.nvm
-git fetch
-git checkout `git describe --abbrev=0 --tags`
-popd
+    pushd ~/.nvm
+    git fetch
+    git checkout `git describe --abbrev=0 --tags`
+    popd
+fi
 
 source ~/.nvm/nvm.sh