add vault 0.8.3 to travis test matrix

Author: evralston

.travis.yml

@@ -4,6 +4,7 @@ language: ruby
 cache: bundler
 
 env:
+  - VAULT_VERSION=0.8.3
   - VAULT_VERSION=0.7.3
   - VAULT_VERSION=0.6.5
   - VAULT_VERSION=0.5.3