Make sure that $ARGS is evaluated natively rather than as a single string argument.

Fixes #494.
diff --git a/nvm.sh b/nvm.sh
index 52bea15..766c607 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -23,7 +23,7 @@
                            -e 's/-s /-q /' \
                            -e 's/-o /-O /' \
                            -e 's/-C - /-c /')
-    wget $ARGS
+    eval wget $ARGS
   fi
 }