Adding a test for `nvm install invalid` behavior, and correcting the message.

From f00d688c87 (commitcomment-6205164)

nvm.sh

@@ -309,7 +309,7 @@ nvm() {
       [ -d "$NVM_DIR/$VERSION" ] && echo "$VERSION is already installed." && return
 
       if [ "$VERSION" = "N/A" ]; then
-        echo "Version '$VERSION' not found - try \`nvm ls-remote\` to browse available versions."
+        echo "Version '$provided_version' not found - try \`nvm ls-remote\` to browse available versions."
         return 3
       fi
 

test/fast/Running "nvm install" with an invalid version fails nicely

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../nvm.sh
+[ "$(nvm install invalid.invalid)" = "Version 'invalid.invalid' not found - try \`nvm ls-remote\` to browse available versions." ] || die "nvm installing an invalid version did not print a nice error message"
+