Ignore errors when sourcing nvm.sh

It fails spuriously if it fails to understand the version of system node.

scripts/test.sh

@@ -233,6 +233,7 @@ trap cleanup EXIT
 
 # Use a consistent version of Node if possible.
 if [[ -z "$(command -v nvm)" ]]; then
+  set +e
   if [ -f "$NVM_DIR/nvm.sh" ]; then
     . "$NVM_DIR/nvm.sh" '' || true
   elif [ -x "$(command -v brew)" ] && [ -f "$(brew --prefix nvm)/nvm.sh" ]; then
@@ -242,6 +243,7 @@ if [[ -z "$(command -v nvm)" ]]; then
   elif [ -f "$HOME/.nvm/nvm.sh" ]; then
     . ~/.nvm/nvm.sh ''
   fi
+  set -e
 fi
 if [[ "$(command -v nvm)" ]]; then
   nvm install 6.5.0