[New] add `nvm cache` with “dir” and “clean” commands.

 - cache the nvm cache on travis
diff --git a/.gitignore b/.gitignore
index 57f44a7..fc578cc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,5 @@
 HEAD
-bin
-src
+.cache
 v*
 alias